diff --git a/bazel/testing/lit.cfg.py b/bazel/testing/lit.cfg.py
new file mode 100644
index 000000000000..7bb56f785475
--- /dev/null
+++ b/bazel/testing/lit.cfg.py
@@ -0,0 +1,56 @@
+__copyright__ = """
+Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+Exceptions. See /LICENSE for license information.
+SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+"""
+
+import lit.formats
+import os
+
+
+# This is a provided variable, ignore the undefined name warning.
+config = config  # noqa: F821
+
+
+def fullpath(relative_path):
+    return os.path.join(os.environ["TEST_SRCDIR"], relative_path)
+
+
+config.name = "lit"
+config.suffixes = [".carbon"]
+config.test_format = lit.formats.ShTest()
+
+config.substitutions.append(
+    (
+        "%{carbon}",
+        fullpath("carbon/toolchain/driver/carbon"),
+    )
+)
+_EXPLORER = "%s --prelude=%s" % (
+    fullpath("carbon/explorer/explorer"),
+    fullpath("carbon/explorer/data/prelude.carbon"),
+)
+config.substitutions.append(("%{explorer}", _EXPLORER))
+config.substitutions.append(
+    ("%{explorer-trace}", _EXPLORER + " --parser_debug --trace_file=-")
+)
+
+config.substitutions.append(("%{not}", fullpath("llvm-project/llvm/not")))
+
+_FILE_CHECK = "%s --dump-input-filter=all" % fullpath(
+    "llvm-project/llvm/FileCheck"
+)
+config.substitutions.append(("%{FileCheck}", _FILE_CHECK))
+config.substitutions.append(
+    (
+        "%{FileCheck-allow-unmatched}",
+        _FILE_CHECK + " --match-full-lines --strict-whitespace",
+    )
+)
+config.substitutions.append(
+    (
+        "%{FileCheck-strict}",
+        _FILE_CHECK
+        + " --implicit-check-not={{.}} --match-full-lines --strict-whitespace",
+    )
+)
diff --git a/explorer/README.md b/explorer/README.md
index 909ed75db1d6..fe1e5ef58e09 100644
--- a/explorer/README.md
+++ b/explorer/README.md
@@ -72,12 +72,10 @@ boilerplate at the top:
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 ```
diff --git a/explorer/interpreter/type_checker.cpp b/explorer/interpreter/type_checker.cpp
index c86050e9aa97..7a1fe96aaa95 100644
--- a/explorer/interpreter/type_checker.cpp
+++ b/explorer/interpreter/type_checker.cpp
@@ -4334,7 +4334,7 @@ auto TypeChecker::CollectMember(Nonnull<const Declaration*> enclosing_decl,
              << enclosing_decl_name
              << " because it clashes with an existing member"
              << " with the same name (declared at " << it->second->source_loc()
-             << ") ";
+             << ")";
     }
   }
   return Success();
diff --git a/explorer/testdata/addr/fail_method_let.carbon b/explorer/testdata/addr/fail_method_let.carbon
index 5e3091a4ac06..a9db15bac7b6 100644
--- a/explorer/testdata/addr/fail_method_let.carbon
+++ b/explorer/testdata/addr/fail_method_let.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -28,7 +26,7 @@ class Point {
 
 fn Main() -> i32 {
   let p: Point = Point.Origin();
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_let.carbon:[[@LINE+1]]: method GetSetX requires its receiver to be an lvalue
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_let.carbon:[[@LINE+1]]: method GetSetX requires its receiver to be an lvalue
   var x: auto = p.GetSetX(42);
   if (p.x == 42) {
     return x;
diff --git a/explorer/testdata/addr/fail_method_me_misspelled.carbon b/explorer/testdata/addr/fail_method_me_misspelled.carbon
index 33506bd84f42..39c13adeabd7 100644
--- a/explorer/testdata/addr/fail_method_me_misspelled.carbon
+++ b/explorer/testdata/addr/fail_method_me_misspelled.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 class C {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_misspelled.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_misspelled.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
   fn F[addr mew: Self*]() {}
 }
 
diff --git a/explorer/testdata/addr/fail_method_me_type.carbon b/explorer/testdata/addr/fail_method_me_type.carbon
index 976ab85adfd4..b560b8f9e491 100644
--- a/explorer/testdata/addr/fail_method_me_type.carbon
+++ b/explorer/testdata/addr/fail_method_me_type.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -32,7 +30,7 @@ class Point {
 
 fn Main() -> i32 {
   var p: Point = Point.Origin();
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_type.carbon:[[@LINE+1]]: type error in method access, receiver type: 'class Point' is not implicitly convertible to 'class Shape'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_type.carbon:[[@LINE+1]]: type error in method access, receiver type: 'class Point' is not implicitly convertible to 'class Shape'
   var x: auto = p.GetSetX(42);
   if (p.x == 42) {
     return x;
diff --git a/explorer/testdata/addr/method.carbon b/explorer/testdata/addr/method.carbon
index c1e70582e070..93e7c57c2398 100644
--- a/explorer/testdata/addr/method.carbon
+++ b/explorer/testdata/addr/method.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/addr/nested_method.carbon b/explorer/testdata/addr/nested_method.carbon
index cf35a423246e..9aca45ba4599 100644
--- a/explorer/testdata/addr/nested_method.carbon
+++ b/explorer/testdata/addr/nested_method.carbon
@@ -3,12 +3,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/alias/class_alias.carbon b/explorer/testdata/alias/class_alias.carbon
index 754fbbe0b710..8406b85d83e2 100644
--- a/explorer/testdata/alias/class_alias.carbon
+++ b/explorer/testdata/alias/class_alias.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: b.n: 1
-// CHECK: d.Get(0): 2
-// CHECK: e.Get(1): 3
-// CHECK: result: 0
+// CHECK:b.n: 1
+// CHECK:d.Get(0): 2
+// CHECK:e.Get(1): 3
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/alias/fail_alias_expression.carbon b/explorer/testdata/alias/fail_alias_expression.carbon
index b37a1e0aa9fd..c6e62a13d548 100644
--- a/explorer/testdata/alias/fail_alias_expression.carbon
+++ b/explorer/testdata/alias/fail_alias_expression.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_alias_expression.carbon:[[@LINE+1]]: invalid target for alias declaration
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_alias_expression.carbon:[[@LINE+1]]: invalid target for alias declaration
 alias A = 5;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/alias/fail_alias_var.carbon b/explorer/testdata/alias/fail_alias_var.carbon
index 3819313dee13..7c37b149ab20 100644
--- a/explorer/testdata/alias/fail_alias_var.carbon
+++ b/explorer/testdata/alias/fail_alias_var.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 var v: i32;
 // TODO: This should probably be valid if we allow global variables at all.
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_alias_var.carbon:[[@LINE+1]]: invalid target for alias declaration
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_alias_var.carbon:[[@LINE+1]]: invalid target for alias declaration
 alias A = v;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/alias/fail_self_alias.carbon b/explorer/testdata/alias/fail_self_alias.carbon
index a04eb5afaf1c..5df90ee6477b 100644
--- a/explorer/testdata/alias/fail_self_alias.carbon
+++ b/explorer/testdata/alias/fail_self_alias.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_self_alias.carbon:[[@LINE+1]]: 'a' is not usable until after it has been completely declared
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_self_alias.carbon:[[@LINE+1]]: 'a' is not usable until after it has been completely declared
 alias a = a;
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/alias/function_alias.carbon b/explorer/testdata/alias/function_alias.carbon
index b05b478eea39..faa9f6bbab06 100644
--- a/explorer/testdata/alias/function_alias.carbon
+++ b/explorer/testdata/alias/function_alias.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 7
+// CHECK:result: 7
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/alias/interface_alias.carbon b/explorer/testdata/alias/interface_alias.carbon
index 8cb3708bffa8..6e63f724d527 100644
--- a/explorer/testdata/alias/interface_alias.carbon
+++ b/explorer/testdata/alias/interface_alias.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 12345
+// CHECK:result: 12345
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/alias/member_name_alias.carbon b/explorer/testdata/alias/member_name_alias.carbon
index f6da101a1a7a..f26084840645 100644
--- a/explorer/testdata/alias/member_name_alias.carbon
+++ b/explorer/testdata/alias/member_name_alias.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/alias/struct_alias.carbon b/explorer/testdata/alias/struct_alias.carbon
index 0a400681c3b3..05e799aca617 100644
--- a/explorer/testdata/alias/struct_alias.carbon
+++ b/explorer/testdata/alias/struct_alias.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: ab.a: 2
-// CHECK: ab.b: 1
-// CHECK: ba.a: 2
-// CHECK: ba.b: 1
-// CHECK: result: 0
+// CHECK:ab.a: 2
+// CHECK:ab.b: 1
+// CHECK:ba.a: 2
+// CHECK:ba.b: 1
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/alias/type_alias.carbon b/explorer/testdata/alias/type_alias.carbon
index 712e2606fb10..01c6eeef4a0e 100644
--- a/explorer/testdata/alias/type_alias.carbon
+++ b/explorer/testdata/alias/type_alias.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 4
+// CHECK:result: 4
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/array/fail_index.carbon b/explorer/testdata/array/fail_index.carbon
index 1f754fa30ad3..ec6caef395b4 100644
--- a/explorer/testdata/array/fail_index.carbon
+++ b/explorer/testdata/array/fail_index.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: [i32; 2] = (0, 1);
-  // CHECK: RUNTIME ERROR: {{.*}}/explorer/testdata/array/fail_index.carbon:[[@LINE+1]]: index 2 out of range in (0, 1)
+  // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/array/fail_index.carbon:[[@LINE+1]]: index 2 out of range in (0, 1)
   return x[2];
 }
diff --git a/explorer/testdata/array/fail_negative_size.carbon b/explorer/testdata/array/fail_negative_size.carbon
index 707e5902ba6b..231eb1f60868 100644
--- a/explorer/testdata/array/fail_negative_size.carbon
+++ b/explorer/testdata/array/fail_negative_size.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/array/fail_negative_size.carbon:[[@LINE+1]]: Array size cannot be negative
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/array/fail_negative_size.carbon:[[@LINE+1]]: Array size cannot be negative
   var x: [i32; -1] = ();
   return x[0];
 }
diff --git a/explorer/testdata/array/fail_size_mismatch.carbon b/explorer/testdata/array/fail_size_mismatch.carbon
index 45693b4ae09a..bfa6b75c223c 100644
--- a/explorer/testdata/array/fail_size_mismatch.carbon
+++ b/explorer/testdata/array/fail_size_mismatch.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/array/fail_size_mismatch.carbon:[[@LINE+1]]: type error in name binding: '(i32, i32, i32)' is not implicitly convertible to '[i32; 2]'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/array/fail_size_mismatch.carbon:[[@LINE+1]]: type error in name binding: '(i32, i32, i32)' is not implicitly convertible to '[i32; 2]'
   var x: [i32; 2] = (0, 1, 2);
   return x[0];
 }
diff --git a/explorer/testdata/array/index.carbon b/explorer/testdata/array/index.carbon
index 5a7e47287b66..4f01243a4b08 100644
--- a/explorer/testdata/array/index.carbon
+++ b/explorer/testdata/array/index.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/array/nested.carbon b/explorer/testdata/array/nested.carbon
index 0043357aeec2..9f04efeaa1e3 100644
--- a/explorer/testdata/array/nested.carbon
+++ b/explorer/testdata/array/nested.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/as/as_same_type.carbon b/explorer/testdata/as/as_same_type.carbon
index 1da2ed4b38aa..d4adee86d1c5 100644
--- a/explorer/testdata/as/as_same_type.carbon
+++ b/explorer/testdata/as/as_same_type.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 5
+// CHECK:result: 5
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/as/convert.carbon b/explorer/testdata/as/convert.carbon
index 0e71efeca677..f27b2636b213 100644
--- a/explorer/testdata/as/convert.carbon
+++ b/explorer/testdata/as/convert.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 5
+// CHECK:result: 5
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/as/fail_destination_not_type.carbon b/explorer/testdata/as/fail_destination_not_type.carbon
index 45190fdf46b5..5b530828d249 100644
--- a/explorer/testdata/as/fail_destination_not_type.carbon
+++ b/explorer/testdata/as/fail_destination_not_type.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/as/fail_destination_not_type.carbon:[[@LINE+1]]: Expected a type, but got 7
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/as/fail_destination_not_type.carbon:[[@LINE+1]]: Expected a type, but got 7
   return 4 as 7;
 }
diff --git a/explorer/testdata/as/fail_no_conversion.carbon b/explorer/testdata/as/fail_no_conversion.carbon
index 6121e783f7de..651388b9a6b8 100644
--- a/explorer/testdata/as/fail_no_conversion.carbon
+++ b/explorer/testdata/as/fail_no_conversion.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +12,7 @@ class A { var n: i32; }
 
 fn Main() -> i32 {
   var a: A = {.n = 5};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/as/fail_no_conversion.carbon:[[@LINE+2]]: type error in `as`: `class A` is not explicitly convertible to `i32`:
-  // CHECK: could not find implementation of interface As(T = i32) for class A
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/as/fail_no_conversion.carbon:[[@LINE+2]]: type error in `as`: `class A` is not explicitly convertible to `i32`:
+  // CHECK:could not find implementation of interface As(T = i32) for class A
   return a as i32;
 }
diff --git a/explorer/testdata/as/implicit_as.carbon b/explorer/testdata/as/implicit_as.carbon
index d2cd3b5aec69..1d679b66f60e 100644
--- a/explorer/testdata/as/implicit_as.carbon
+++ b/explorer/testdata/as/implicit_as.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 5
+// CHECK:result: 5
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assert/assert.carbon b/explorer/testdata/assert/assert.carbon
index b0469104e5c6..39ed0c87082b 100644
--- a/explorer/testdata/assert/assert.carbon
+++ b/explorer/testdata/assert/assert.carbon
@@ -5,12 +5,10 @@
 // This won't auto-update because it uses a regex for the prelude line number,
 // so that it doesn't need to be updated on every prelude change.
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // NOAUTOUPDATE
-// CHECK: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: "HALLO WELT"
+// CHECK:RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: "HALLO WELT"
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assign/convert_rhs.carbon b/explorer/testdata/assign/convert_rhs.carbon
index 2bdd5b5ef9f9..febb9d6d4259 100644
--- a/explorer/testdata/assign/convert_rhs.carbon
+++ b/explorer/testdata/assign/convert_rhs.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assign/destruct_original.carbon b/explorer/testdata/assign/destruct_original.carbon
index 821370954a28..9c1a61d022a1 100644
--- a/explorer/testdata/assign/destruct_original.carbon
+++ b/explorer/testdata/assign/destruct_original.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assign/reassign_original.carbon b/explorer/testdata/assign/reassign_original.carbon
index b73232afa5e0..881a94da90cf 100644
--- a/explorer/testdata/assign/reassign_original.carbon
+++ b/explorer/testdata/assign/reassign_original.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assoc_const/fail_anonymous.carbon b/explorer/testdata/assoc_const/fail_anonymous.carbon
index 4a12a0f09493..8a4b5ed58778 100644
--- a/explorer/testdata/assoc_const/fail_anonymous.carbon
+++ b/explorer/testdata/assoc_const/fail_anonymous.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 interface Iface {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/assoc_const/fail_anonymous.carbon:[[@LINE+1]]: syntax error, unexpected UNDERSCORE, expecting identifier
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/assoc_const/fail_anonymous.carbon:[[@LINE+1]]: syntax error, unexpected UNDERSCORE, expecting identifier
   let _:! Type;
 }
 
diff --git a/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon b/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon
index f933a915e517..01a6c23fb856 100644
--- a/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon
+++ b/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ interface HasThreeTypes {
   let C:! Type;
 }
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon:[[@LINE+1]]: implementation missing (.Self:! HasThreeTypes).B
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon:[[@LINE+1]]: implementation missing (.Self:! HasThreeTypes).B
 external impl i32 as HasThreeTypes where .A == i32 and .C == i32 {}
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon b/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon
index c45857f2d5a3..82af6707ffeb 100644
--- a/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon
+++ b/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ interface HasThreeTypes {
   let C:! Type;
 }
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon:[[@LINE+1]]: implementation doesn't provide a concrete value for (.Self:! HasThreeTypes).B
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon:[[@LINE+1]]: implementation doesn't provide a concrete value for (.Self:! HasThreeTypes).B
 external impl i32 as HasThreeTypes where .A == i32 and .B == .C {}
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/assoc_const/fail_indirectly_equal.carbon b/explorer/testdata/assoc_const/fail_indirectly_equal.carbon
index 9620c4ae4f78..4afbd6845c1a 100644
--- a/explorer/testdata/assoc_const/fail_indirectly_equal.carbon
+++ b/explorer/testdata/assoc_const/fail_indirectly_equal.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -25,7 +23,7 @@ fn F2[U:! A where .T == i32](x: i32) -> U.T {
 }
 
 fn F3[T:! A where .T == i32, U:! A where .T == i32](x: T.T) -> U.T {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_indirectly_equal.carbon:[[@LINE+1]]: type error in return value: '(T:! A where .Self.T == i32).T' is not implicitly convertible to '(U:! A where .Self.T == i32).T'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_indirectly_equal.carbon:[[@LINE+1]]: type error in return value: '(T:! A where .Self.T == i32).T' is not implicitly convertible to '(U:! A where .Self.T == i32).T'
   return x;
 }
 
diff --git a/explorer/testdata/assoc_const/fail_match_in_deduction.carbon b/explorer/testdata/assoc_const/fail_match_in_deduction.carbon
index b6b96f6bdf10..f16a0f378408 100644
--- a/explorer/testdata/assoc_const/fail_match_in_deduction.carbon
+++ b/explorer/testdata/assoc_const/fail_match_in_deduction.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 // TODO: Should this work?
@@ -24,7 +22,7 @@ fn F[Scalar:! Type, V:! Vector where .Dim == 3](p: Point(Scalar, V.Dim), v: V) {
 fn G[Scalar:! Type](p: Point(Scalar, 3)) {}
 fn H[V:! Vector where .Dim == 3](v: V) {
   var p: Point(i32, V.Dim) = {};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_match_in_deduction.carbon:[[@LINE+1]]: mismatch in non-type values, `(V:! Vector where .Self.Dim == 3).Dim` != `3`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_match_in_deduction.carbon:[[@LINE+1]]: mismatch in non-type values, `(V:! Vector where .Self.Dim == 3).Dim` != `3`
   G(p);
 }
 
diff --git a/explorer/testdata/assoc_const/fail_multi_impl_scoping.carbon b/explorer/testdata/assoc_const/fail_multi_impl_scoping.carbon
index 4b18ce1a9f93..59078106d467 100644
--- a/explorer/testdata/assoc_const/fail_multi_impl_scoping.carbon
+++ b/explorer/testdata/assoc_const/fail_multi_impl_scoping.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -40,7 +38,7 @@ class C(T:! Type) {
 
 external impl C(i32) as B where .TB == () {
   fn FB() -> () { return (); }
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_multi_impl_scoping.carbon:[[@LINE+1]]: ambiguous implementations of interface B for class C(T = i32)
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_multi_impl_scoping.carbon:[[@LINE+1]]: ambiguous implementations of interface B for class C(T = i32)
 }
 
 fn Main() -> i32 { return C(i32).FB(); }
diff --git a/explorer/testdata/assoc_const/fail_multiple_deduction.carbon b/explorer/testdata/assoc_const/fail_multiple_deduction.carbon
index 7c36edf00848..c9a2b75846fa 100644
--- a/explorer/testdata/assoc_const/fail_multiple_deduction.carbon
+++ b/explorer/testdata/assoc_const/fail_multiple_deduction.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -18,9 +16,9 @@ interface HasThreeTypes {
 }
 fn F[T:! Type](x: (T, T, T));
 fn G[X:! HasThreeTypes where .A == .B and .B == .C and .C == .A](x: X) {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_multiple_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! Type:
-  // CHECK:   (X:! HasThreeTypes where .Self.A == .Self.B and .Self.B == .Self.C and .Self.C == .Self.A).A
-  // CHECK:   (X:! HasThreeTypes where .Self.A == .Self.B and .Self.B == .Self.C and .Self.C == .Self.A).B
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_multiple_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! Type:
+  // CHECK:  (X:! HasThreeTypes where .Self.A == .Self.B and .Self.B == .Self.C and .Self.C == .Self.A).A
+  // CHECK:  (X:! HasThreeTypes where .Self.A == .Self.B and .Self.B == .Self.C and .Self.C == .Self.A).B
   F(x.Make());
 }
 
diff --git a/explorer/testdata/assoc_const/fail_overspecified_impl.carbon b/explorer/testdata/assoc_const/fail_overspecified_impl.carbon
index 122443b221e7..01bce3dfcad0 100644
--- a/explorer/testdata/assoc_const/fail_overspecified_impl.carbon
+++ b/explorer/testdata/assoc_const/fail_overspecified_impl.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +12,7 @@ interface HasType {
   let T:! Type;
 }
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_overspecified_impl.carbon:[[@LINE+1]]: implementation provides multiple values for (.Self:! HasType).T: i32 and {.a: i32}
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_overspecified_impl.carbon:[[@LINE+1]]: implementation provides multiple values for (.Self:! HasType).T: i32 and {.a: i32}
 external impl i32 as HasType where .T == i32 and .T == {.a: i32} {}
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/assoc_const/fail_redefined.carbon b/explorer/testdata/assoc_const/fail_redefined.carbon
index 25a9afd9943e..2ef671524c1d 100644
--- a/explorer/testdata/assoc_const/fail_redefined.carbon
+++ b/explorer/testdata/assoc_const/fail_redefined.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 interface Iface {
   let T:! Type;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_redefined.carbon:[[@LINE+1]]: Duplicate name `T` also found at {{.*}}/explorer/testdata/assoc_const/fail_redefined.carbon:14
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_redefined.carbon:[[@LINE+1]]: Duplicate name `T` also found at {{.*}}/explorer/testdata/assoc_const/fail_redefined.carbon:12
   let T:! Type;
 }
 
diff --git a/explorer/testdata/assoc_const/fail_unknown_value.carbon b/explorer/testdata/assoc_const/fail_unknown_value.carbon
index 81ade90902b2..1ceecaedab9b 100644
--- a/explorer/testdata/assoc_const/fail_unknown_value.carbon
+++ b/explorer/testdata/assoc_const/fail_unknown_value.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,7 +13,7 @@ interface Iface { let N:! i32; }
 fn PickType(N: i32) -> Type { return i32; }
 
 fn F[T:! Iface](x: T) -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_unknown_value.carbon:[[@LINE+1]]: value of associated constant (T:! Iface).N is not known
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_unknown_value.carbon:[[@LINE+1]]: value of associated constant (T:! Iface).N is not known
   var x: PickType(T.N) = 0;
   return x;
 }
diff --git a/explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon b/explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon
index 999b6c0b6e06..9ad53998bf78 100644
--- a/explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon
+++ b/explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ fn PickType(N: i32) -> Type { return i32; }
 
 fn F[T:! Iface where .N == 5](x: T) -> i32 {
   // TODO: This should be valid: the value of T.N is known to be 5 here.
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon:[[@LINE+1]]: value of associated constant (T:! Iface where .Self.N == 5).N is not known
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon:[[@LINE+1]]: value of associated constant (T:! Iface where .Self.N == 5).N is not known
   var x: PickType(T.N) = 0;
   return x;
 }
diff --git a/explorer/testdata/assoc_const/impl_lookup.carbon b/explorer/testdata/assoc_const/impl_lookup.carbon
index 542fa80daec6..168032caaa83 100644
--- a/explorer/testdata/assoc_const/impl_lookup.carbon
+++ b/explorer/testdata/assoc_const/impl_lookup.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assoc_const/implement.carbon b/explorer/testdata/assoc_const/implement.carbon
index 8becf1f49ed3..2daf740a1ec4 100644
--- a/explorer/testdata/assoc_const/implement.carbon
+++ b/explorer/testdata/assoc_const/implement.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 2
+// CHECK:result: 2
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assoc_const/simple_constraint.carbon b/explorer/testdata/assoc_const/simple_constraint.carbon
index e6998b8e86bc..b370dbebc6b5 100644
--- a/explorer/testdata/assoc_const/simple_constraint.carbon
+++ b/explorer/testdata/assoc_const/simple_constraint.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assoc_const/simple_equality.carbon b/explorer/testdata/assoc_const/simple_equality.carbon
index 25736ebda1b3..61277a82c330 100644
--- a/explorer/testdata/assoc_const/simple_equality.carbon
+++ b/explorer/testdata/assoc_const/simple_equality.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/basic_syntax/addition.carbon b/explorer/testdata/basic_syntax/addition.carbon
index 29666b44af66..4fb6dd1080a9 100644
--- a/explorer/testdata/basic_syntax/addition.carbon
+++ b/explorer/testdata/basic_syntax/addition.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 7
+// CHECK:result: 7
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/basic_syntax/choice.carbon b/explorer/testdata/basic_syntax/choice.carbon
index 6303f275b241..fa9f059d5a14 100644
--- a/explorer/testdata/basic_syntax/choice.carbon
+++ b/explorer/testdata/basic_syntax/choice.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon b/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon
index c08e81614ed0..9fe4356cbac0 100644
--- a/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon
+++ b/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon:[[@LINE+1]]: Expected a type, but got (42)
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon:[[@LINE+1]]: Expected a type, but got (42)
 choice C { X(42) }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon b/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon
index c692fc6ef035..bad56a3b8617 100644
--- a/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon
+++ b/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 choice Ch {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon:[[@LINE+1]]: 'Ch' is not usable until after it has been completely declared
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon:[[@LINE+1]]: 'Ch' is not usable until after it has been completely declared
   Opt(Ch)
 }
 
diff --git a/explorer/testdata/basic_syntax/fail_assign_to_function.carbon b/explorer/testdata/basic_syntax/fail_assign_to_function.carbon
index 3c8cbf50e189..137a317cfb57 100644
--- a/explorer/testdata/basic_syntax/fail_assign_to_function.carbon
+++ b/explorer/testdata/basic_syntax/fail_assign_to_function.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +12,7 @@ fn F() {}
 fn G() {}
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_assign_to_function.carbon:[[@LINE+1]]: Cannot assign to rvalue 'F'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_assign_to_function.carbon:[[@LINE+1]]: Cannot assign to rvalue 'F'
   F = G;
   return 0;
 }
diff --git a/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon b/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon
index 3c3e33f261b3..a158b46871ec 100644
--- a/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon
+++ b/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon:[[@LINE+1]]: Cannot assign to rvalue '1'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon:[[@LINE+1]]: Cannot assign to rvalue '1'
   1 = 0;
   return 0;
 }
diff --git a/explorer/testdata/basic_syntax/fail_block.carbon b/explorer/testdata/basic_syntax/fail_block.carbon
index 0b7e88f43532..b8db4a04df13 100644
--- a/explorer/testdata/basic_syntax/fail_block.carbon
+++ b/explorer/testdata/basic_syntax/fail_block.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   {
-    // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_block.carbon:[[@LINE+1]]: syntax error, unexpected RETURN, expecting PERIOD or RIGHT_CURLY_BRACE
+    // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_block.carbon:[[@LINE+1]]: syntax error, unexpected RETURN, expecting PERIOD or RIGHT_CURLY_BRACE
     return 0;
   }
 }
diff --git a/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon b/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon
index 5780bb05a801..cab244465619 100644
--- a/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon
+++ b/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -19,9 +17,9 @@ choice Ints {
 fn Main() -> i32 {
   match (Ints.None()) {
     case Ints.None => { return 0; }
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon:[[@LINE+3]]: type error in `match` pattern type
-    // CHECK: expected: fn () -> choice Ints
-    // CHECK: actual: choice Ints
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon:[[@LINE+3]]: type error in `match` pattern type
+    // CHECK:expected: fn () -> choice Ints
+    // CHECK:actual: choice Ints
     default => { return 1; }
   }
 }
diff --git a/explorer/testdata/basic_syntax/fail_invalid_char.carbon b/explorer/testdata/basic_syntax/fail_invalid_char.carbon
index d430ea7af2d4..5d7f93f703bd 100644
--- a/explorer/testdata/basic_syntax/fail_invalid_char.carbon
+++ b/explorer/testdata/basic_syntax/fail_invalid_char.carbon
@@ -2,11 +2,9 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
-// CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_char.carbon:[[@LINE+1]]: invalid character '\xEF' in source file.
+// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_char.carbon:[[@LINE+1]]: invalid character '\xEF' in source file.
 �
diff --git a/explorer/testdata/basic_syntax/fail_invalid_integer.carbon b/explorer/testdata/basic_syntax/fail_invalid_integer.carbon
index 76f987fc9568..a41884fdbec3 100644
--- a/explorer/testdata/basic_syntax/fail_invalid_integer.carbon
+++ b/explorer/testdata/basic_syntax/fail_invalid_integer.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_integer.carbon:[[@LINE+1]]: Invalid integer literal: 11111111111111111111111111
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_integer.carbon:[[@LINE+1]]: Invalid integer literal: 11111111111111111111111111
   return 11111111111111111111111111;
 }
diff --git a/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon b/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon
index d642e1e89cc5..f5d34f4f8e89 100644
--- a/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon
+++ b/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon:[[@LINE+1]]: Invalid type literal: i11111111111111111111111111
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon:[[@LINE+1]]: Invalid type literal: i11111111111111111111111111
   var x: i11111111111111111111111111 = 1;
   return 0;
 }
diff --git a/explorer/testdata/basic_syntax/fail_invalid_var_expression.carbon b/explorer/testdata/basic_syntax/fail_invalid_var_expression.carbon
index 5480e1d1f477..4c4aaac9b05d 100644
--- a/explorer/testdata/basic_syntax/fail_invalid_var_expression.carbon
+++ b/explorer/testdata/basic_syntax/fail_invalid_var_expression.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_var_expression.carbon:[[@LINE+1]]: Expected expression for variable type
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_var_expression.carbon:[[@LINE+1]]: Expected expression for variable type
 var a: auto;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/basic_syntax/fail_missing_var.carbon b/explorer/testdata/basic_syntax/fail_missing_var.carbon
index 67f6d584cbf7..66881e7a2194 100644
--- a/explorer/testdata/basic_syntax/fail_missing_var.carbon
+++ b/explorer/testdata/basic_syntax/fail_missing_var.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   // error
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_missing_var.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_missing_var.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
   x : i32;
   return 1;
 }
diff --git a/explorer/testdata/basic_syntax/fail_nested_binding.carbon b/explorer/testdata/basic_syntax/fail_nested_binding.carbon
index 6b305c7d5878..114cfb719bc7 100644
--- a/explorer/testdata/basic_syntax/fail_nested_binding.carbon
+++ b/explorer/testdata/basic_syntax/fail_nested_binding.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_nested_binding.carbon:[[@LINE+1]]: The type of a binding pattern cannot contain bindings.
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_nested_binding.carbon:[[@LINE+1]]: The type of a binding pattern cannot contain bindings.
   var x: (T: Type) = 1;
   return 1;
 }
diff --git a/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon b/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon
index 6cf2b05b0cb2..6e2cbc6cf8c5 100644
--- a/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon
+++ b/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon:[[@LINE+1]]: Unimplemented
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon:[[@LINE+1]]: Unimplemented
   return 1 __unimplemented_example_infix 2;
 }
diff --git a/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon b/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon
index 65c6baf84821..f27effd02bdf 100644
--- a/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon
+++ b/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon:[[@LINE+1]]: Unknown intrinsic 'nonexistent'
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon:[[@LINE+1]]: Unknown intrinsic 'nonexistent'
   return __intrinsic_nonexistent();
 }
diff --git a/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon b/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon
index fb17e15a1e6b..39ccc4b48fba 100644
--- a/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon
+++ b/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon:[[@LINE+1]]: Only i32 is supported for now: i64
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon:[[@LINE+1]]: Only i32 is supported for now: i64
   var x: i64 = 1;
   return 0;
 }
diff --git a/explorer/testdata/basic_syntax/fail_var_named_self.carbon b/explorer/testdata/basic_syntax/fail_var_named_self.carbon
index fbc7803c1f20..474261a6e454 100644
--- a/explorer/testdata/basic_syntax/fail_var_named_self.carbon
+++ b/explorer/testdata/basic_syntax/fail_var_named_self.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +12,7 @@ fn Main() -> i32 {
   // Error: can't use keyword `Self` as the name of a variable.
   // TODO: Current error message is unclear, better would be to say
   // something like: unexpected `Self`, expecting identifier
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_var_named_self.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_var_named_self.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
   var Self : i32 = 0;
   return Self;
 }
diff --git a/explorer/testdata/basic_syntax/fail_var_type.carbon b/explorer/testdata/basic_syntax/fail_var_type.carbon
index b0b21eed5d68..70c92ec77dbd 100644
--- a/explorer/testdata/basic_syntax/fail_var_type.carbon
+++ b/explorer/testdata/basic_syntax/fail_var_type.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn Main () -> i32
 {
   // 42 cannot be used as the type of a variable.
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_var_type.carbon:[[@LINE+1]]: Expected a type, but got 42
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_var_type.carbon:[[@LINE+1]]: Expected a type, but got 42
   var x: 42 = 0;
   return x;
 }
diff --git a/explorer/testdata/basic_syntax/next.carbon b/explorer/testdata/basic_syntax/next.carbon
index 2ec3c04232a4..e1f190470b1e 100644
--- a/explorer/testdata/basic_syntax/next.carbon
+++ b/explorer/testdata/basic_syntax/next.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/basic_syntax/not_compare_precedence.carbon b/explorer/testdata/basic_syntax/not_compare_precedence.carbon
index bfc37609b026..b64af43f52a6 100644
--- a/explorer/testdata/basic_syntax/not_compare_precedence.carbon
+++ b/explorer/testdata/basic_syntax/not_compare_precedence.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn CompareBools(a: bool, b: bool) -> bool {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/not_compare_precedence.carbon:[[@LINE+1]]: syntax error, unexpected EQUAL_EQUAL, expecting SEMICOLON
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/not_compare_precedence.carbon:[[@LINE+1]]: syntax error, unexpected EQUAL_EQUAL, expecting SEMICOLON
   return not a == b;
 }
diff --git a/explorer/testdata/basic_syntax/placeholder_variable.carbon b/explorer/testdata/basic_syntax/placeholder_variable.carbon
index 8e0d58dbcb75..160e6f97a75d 100644
--- a/explorer/testdata/basic_syntax/placeholder_variable.carbon
+++ b/explorer/testdata/basic_syntax/placeholder_variable.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/basic_syntax/record.carbon b/explorer/testdata/basic_syntax/record.carbon
index 1612cbbeee72..0e98a6b28082 100644
--- a/explorer/testdata/basic_syntax/record.carbon
+++ b/explorer/testdata/basic_syntax/record.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/basic_syntax/star.carbon b/explorer/testdata/basic_syntax/star.carbon
index 3fce44e856e7..561ff07b8116 100644
--- a/explorer/testdata/basic_syntax/star.carbon
+++ b/explorer/testdata/basic_syntax/star.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/basic_syntax/trace.carbon b/explorer/testdata/basic_syntax/trace.carbon
index b38caa4626ee..3a68cc0122d7 100644
--- a/explorer/testdata/basic_syntax/trace.carbon
+++ b/explorer/testdata/basic_syntax/trace.carbon
@@ -2,25 +2,24 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 //
 // A lot of output is elided: this is only checking for a few things for simple
 // sanity checking on --parser_debug --trace_file=- output.
 //
 // NOAUTOUPDATE
-// CHECK: ********** source program **********
-// CHECK: interface ImplicitAs {
-// CHECK: ********** type checking **********
-// CHECK: ** declaring interface ImplicitAs
-// CHECK: ********** resolving unformed variables **********
-// CHECK: ********** printing declarations **********
-// CHECK: interface ImplicitAs {
-// CHECK: ********** starting execution **********
-// CHECK: ********** initializing globals **********
-// CHECK: ********** calling main function **********
-// CHECK: --- step exp Main() .0. (<Main()>:0) --->
-// CHECK: result: 0
+// CHECK:********** source program **********
+// CHECK:interface ImplicitAs {
+// CHECK:********** type checking **********
+// CHECK:** declaring interface ImplicitAs
+// CHECK:********** resolving unformed variables **********
+// CHECK:********** printing declarations **********
+// CHECK:interface ImplicitAs {
+// CHECK:********** starting execution **********
+// CHECK:********** initializing globals **********
+// CHECK:********** calling main function **********
+// CHECK:--- step exp Main() .0. (<Main()>:0) --->
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/basic_syntax/var_tuple.carbon b/explorer/testdata/basic_syntax/var_tuple.carbon
index b3c503a823fe..28101557560f 100644
--- a/explorer/testdata/basic_syntax/var_tuple.carbon
+++ b/explorer/testdata/basic_syntax/var_tuple.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/basic_syntax/zero.carbon b/explorer/testdata/basic_syntax/zero.carbon
index ceccaab4a654..cadff806651e 100644
--- a/explorer/testdata/basic_syntax/zero.carbon
+++ b/explorer/testdata/basic_syntax/zero.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/block/empty.carbon b/explorer/testdata/block/empty.carbon
index b10b299358bc..8bddf9538e05 100644
--- a/explorer/testdata/block/empty.carbon
+++ b/explorer/testdata/block/empty.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/block/shadowing.carbon b/explorer/testdata/block/shadowing.carbon
index b6bdaa724b55..71c9187d315e 100644
--- a/explorer/testdata/block/shadowing.carbon
+++ b/explorer/testdata/block/shadowing.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/choice/generic_choice_multiple_template_arguments.carbon b/explorer/testdata/choice/generic_choice_multiple_template_arguments.carbon
index 02948a04988f..192d99216d7d 100644
--- a/explorer/testdata/choice/generic_choice_multiple_template_arguments.carbon
+++ b/explorer/testdata/choice/generic_choice_multiple_template_arguments.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 22
+// CHECK:result: 22
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/choice/generic_choice_nested_in_template_class.carbon b/explorer/testdata/choice/generic_choice_nested_in_template_class.carbon
index 93a0a9fe5d25..0f213d3534d4 100644
--- a/explorer/testdata/choice/generic_choice_nested_in_template_class.carbon
+++ b/explorer/testdata/choice/generic_choice_nested_in_template_class.carbon
@@ -2,13 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: H 22
-// CHECK: result: 0
+// CHECK:H 22
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/choice/generic_choice_simple_assignment.carbon b/explorer/testdata/choice/generic_choice_simple_assignment.carbon
index 6b9f00fc2f13..8190ae220573 100644
--- a/explorer/testdata/choice/generic_choice_simple_assignment.carbon
+++ b/explorer/testdata/choice/generic_choice_simple_assignment.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 22
+// CHECK:result: 22
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/assign.carbon b/explorer/testdata/class/assign.carbon
index fad9ea710496..4225afa83f3e 100644
--- a/explorer/testdata/class/assign.carbon
+++ b/explorer/testdata/class/assign.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/assign_member.carbon b/explorer/testdata/class/assign_member.carbon
index e1d73002897c..36c2ef3ef74b 100644
--- a/explorer/testdata/class/assign_member.carbon
+++ b/explorer/testdata/class/assign_member.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/bound_method.carbon b/explorer/testdata/class/bound_method.carbon
index 0d73ebed84eb..9d18fada7646 100644
--- a/explorer/testdata/class/bound_method.carbon
+++ b/explorer/testdata/class/bound_method.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/class_function.carbon b/explorer/testdata/class/class_function.carbon
index c5a813c38988..c3866c400e2a 100644
--- a/explorer/testdata/class/class_function.carbon
+++ b/explorer/testdata/class/class_function.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/class_function_from_instance.carbon b/explorer/testdata/class/class_function_from_instance.carbon
index db21ba27d4db..0a3de685e89a 100644
--- a/explorer/testdata/class/class_function_from_instance.carbon
+++ b/explorer/testdata/class/class_function_from_instance.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/class_function_self.carbon b/explorer/testdata/class/class_function_self.carbon
index 0f1aa6e85bc2..757922ba7b60 100644
--- a/explorer/testdata/class/class_function_self.carbon
+++ b/explorer/testdata/class/class_function_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/class_function_value.carbon b/explorer/testdata/class/class_function_value.carbon
index 15d70cf5d569..0fe9ec00f75a 100644
--- a/explorer/testdata/class/class_function_value.carbon
+++ b/explorer/testdata/class/class_function_value.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/empty_class.carbon b/explorer/testdata/class/empty_class.carbon
index 3133a683c777..d877358eb5a1 100644
--- a/explorer/testdata/class/empty_class.carbon
+++ b/explorer/testdata/class/empty_class.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/fail_abstract_class.carbon b/explorer/testdata/class/fail_abstract_class.carbon
index aae01dd79890..5eb3f03d927c 100644
--- a/explorer/testdata/class/fail_abstract_class.carbon
+++ b/explorer/testdata/class/fail_abstract_class.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 abstract class C {
   fn F() {}
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_abstract_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_abstract_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/class/fail_base_class.carbon b/explorer/testdata/class/fail_base_class.carbon
index a22d39e113a9..37163632be3e 100644
--- a/explorer/testdata/class/fail_base_class.carbon
+++ b/explorer/testdata/class/fail_base_class.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 base class C {
   fn F() {}
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_base_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_base_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/class/fail_class_extends.carbon b/explorer/testdata/class/fail_class_extends.carbon
index fba1c7013991..ffcc95b32358 100644
--- a/explorer/testdata/class/fail_class_extends.carbon
+++ b/explorer/testdata/class/fail_class_extends.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ class A {
 
 class B extends A {
   fn F() {}
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_class_extends.carbon:[[@LINE+1]]: Class extension with `extends` is not supported yet
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_class_extends.carbon:[[@LINE+1]]: Class extension with `extends` is not supported yet
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/class/fail_class_named_self.carbon b/explorer/testdata/class/fail_class_named_self.carbon
index e65f677a9744..0a3de792cb42 100644
--- a/explorer/testdata/class/fail_class_named_self.carbon
+++ b/explorer/testdata/class/fail_class_named_self.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 // Error: Can't use keyword `Self` as the name of a class.
-// CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/class/fail_class_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
+// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/class/fail_class_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
 class Self {
   var x: i32;
   var y: i32;
diff --git a/explorer/testdata/class/fail_field_access_mismatch.carbon b/explorer/testdata/class/fail_field_access_mismatch.carbon
index eb2db096a42f..40cb7841e665 100644
--- a/explorer/testdata/class/fail_field_access_mismatch.carbon
+++ b/explorer/testdata/class/fail_field_access_mismatch.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -17,6 +15,6 @@ class Point {
 
 fn Main() -> i32 {
   var p: Point = {.x = 1, .y = 2};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_access_mismatch.carbon:[[@LINE+1]]: class Point does not have a field named z
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_access_mismatch.carbon:[[@LINE+1]]: class Point does not have a field named z
   return p.z - 1;
 }
diff --git a/explorer/testdata/class/fail_field_mismatch.carbon b/explorer/testdata/class/fail_field_mismatch.carbon
index d1791463a20b..173ad477606b 100644
--- a/explorer/testdata/class/fail_field_mismatch.carbon
+++ b/explorer/testdata/class/fail_field_mismatch.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_mismatch.carbon:[[@LINE+1]]: type error in name binding: '{.x: i32, .z: i32}' is not implicitly convertible to 'class Point'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_mismatch.carbon:[[@LINE+1]]: type error in name binding: '{.x: i32, .z: i32}' is not implicitly convertible to 'class Point'
   var p: Point = {.x = 1, .z = 2};
   return p.x - 1;
 }
diff --git a/explorer/testdata/class/fail_field_missing.carbon b/explorer/testdata/class/fail_field_missing.carbon
index 37d3795386d0..7cfa17de9810 100644
--- a/explorer/testdata/class/fail_field_missing.carbon
+++ b/explorer/testdata/class/fail_field_missing.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_missing.carbon:[[@LINE+1]]: type error in name binding: '{.x: i32}' is not implicitly convertible to 'class Point'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_missing.carbon:[[@LINE+1]]: type error in name binding: '{.x: i32}' is not implicitly convertible to 'class Point'
   var p: Point = {.x = 1};
   return p.x - 1;
 }
diff --git a/explorer/testdata/class/fail_method_deduced.carbon b/explorer/testdata/class/fail_method_deduced.carbon
index f011182006db..b7084bccfd93 100644
--- a/explorer/testdata/class/fail_method_deduced.carbon
+++ b/explorer/testdata/class/fail_method_deduced.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -19,7 +17,7 @@ fn H[T:! Type](x: T) {}
 
 fn Main() -> i32 {
   H(C.F);
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_method_deduced.carbon:[[@LINE+1]]: Expected a type, but got member name G
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_method_deduced.carbon:[[@LINE+1]]: Expected a type, but got member name G
   H(C.G);
   return 0;
 }
diff --git a/explorer/testdata/class/fail_method_from_class.carbon b/explorer/testdata/class/fail_method_from_class.carbon
index 414747b9f08e..1fe7507da879 100644
--- a/explorer/testdata/class/fail_method_from_class.carbon
+++ b/explorer/testdata/class/fail_method_from_class.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -24,6 +22,6 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_method_from_class.carbon:[[@LINE+1]]: in call `Point.GetX()`, expected callee to be a function, found `member name GetX`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_method_from_class.carbon:[[@LINE+1]]: in call `Point.GetX()`, expected callee to be a function, found `member name GetX`
   return Point.GetX();
 }
diff --git a/explorer/testdata/class/fail_method_in_var.carbon b/explorer/testdata/class/fail_method_in_var.carbon
index 58cfdfd42bbf..6b8cde19cd30 100644
--- a/explorer/testdata/class/fail_method_in_var.carbon
+++ b/explorer/testdata/class/fail_method_in_var.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -17,7 +15,7 @@ class C {
 
 fn Main() -> i32 {
   var f: auto = C.F;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_method_in_var.carbon:[[@LINE+1]]: Expected a type, but got member name G
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_method_in_var.carbon:[[@LINE+1]]: Expected a type, but got member name G
   var g: auto = C.G;
 
   return 0;
diff --git a/explorer/testdata/class/fail_return_method.carbon b/explorer/testdata/class/fail_return_method.carbon
index ef6e05ecf013..147bbe71a20f 100644
--- a/explorer/testdata/class/fail_return_method.carbon
+++ b/explorer/testdata/class/fail_return_method.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ class C {
 }
 
 fn ReturnF() -> auto { return C.F; }
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_return_method.carbon:[[@LINE+1]]: Expected a type, but got member name G
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_return_method.carbon:[[@LINE+1]]: Expected a type, but got member name G
 fn ReturnG() -> auto { return C.G; }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/class/function_param.carbon b/explorer/testdata/class/function_param.carbon
index 12c66fbbe0ba..b210109ce4d5 100644
--- a/explorer/testdata/class/function_param.carbon
+++ b/explorer/testdata/class/function_param.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/global_var.carbon b/explorer/testdata/class/global_var.carbon
index 7ba15504f2d8..a09930d1ed62 100644
--- a/explorer/testdata/class/global_var.carbon
+++ b/explorer/testdata/class/global_var.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/method.carbon b/explorer/testdata/class/method.carbon
index 64871158213b..876cfe2d4995 100644
--- a/explorer/testdata/class/method.carbon
+++ b/explorer/testdata/class/method.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/method_call_method.carbon b/explorer/testdata/class/method_call_method.carbon
index dd72eb81846e..1e52aa1681b0 100644
--- a/explorer/testdata/class/method_call_method.carbon
+++ b/explorer/testdata/class/method_call_method.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/method_self.carbon b/explorer/testdata/class/method_self.carbon
index af7a184e0aaa..c079a9b89c5b 100644
--- a/explorer/testdata/class/method_self.carbon
+++ b/explorer/testdata/class/method_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/temp.carbon b/explorer/testdata/class/temp.carbon
index d64a203c561c..48f83df76f8a 100644
--- a/explorer/testdata/class/temp.carbon
+++ b/explorer/testdata/class/temp.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/class/var.carbon b/explorer/testdata/class/var.carbon
index ab70055f5f9f..9acfbd7ccf6d 100644
--- a/explorer/testdata/class/var.carbon
+++ b/explorer/testdata/class/var.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/comparison/builtin_comparsion.carbon b/explorer/testdata/comparison/builtin_comparsion.carbon
index 5dddd2c890e2..1a70a679b9f4 100644
--- a/explorer/testdata/comparison/builtin_comparsion.carbon
+++ b/explorer/testdata/comparison/builtin_comparsion.carbon
@@ -2,20 +2,18 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: strings less: 1
-// CHECK: ints less: 0
-// CHECK: strings less eq: 1
-// CHECK: ints less eq: 1
-// CHECK: strings greater: 0
-// CHECK: ints greater: 0
-// CHECK: strings greater eq: 0
-// CHECK: ints greater eq: 1
-// CHECK: result: 0
+// CHECK:strings less: 1
+// CHECK:ints less: 0
+// CHECK:strings less eq: 1
+// CHECK:ints less eq: 1
+// CHECK:strings greater: 0
+// CHECK:ints greater: 0
+// CHECK:strings greater eq: 0
+// CHECK:ints greater eq: 1
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/comparison/builtin_equality.carbon b/explorer/testdata/comparison/builtin_equality.carbon
index 601f5da50bce..0a12b1d34bc3 100644
--- a/explorer/testdata/comparison/builtin_equality.carbon
+++ b/explorer/testdata/comparison/builtin_equality.carbon
@@ -2,36 +2,34 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: bool: 1
-// CHECK: bool: 1
-// CHECK: bool: 1
-// CHECK: bool: 1
-// CHECK: bool: 1
-// CHECK: bool: 1
-// CHECK: bool: 1
-// CHECK: bool: 1
-// CHECK: string: 1
-// CHECK: string: 1
-// CHECK: string: 1
-// CHECK: string: 1
-// CHECK: string: 1
-// CHECK: string: 1
-// CHECK: string: 1
-// CHECK: string: 1
-// CHECK: int: 1
-// CHECK: int: 1
-// CHECK: int: 1
-// CHECK: int: 1
-// CHECK: int: 1
-// CHECK: int: 1
-// CHECK: int: 1
-// CHECK: int: 1
-// CHECK: result: 0
+// CHECK:bool: 1
+// CHECK:bool: 1
+// CHECK:bool: 1
+// CHECK:bool: 1
+// CHECK:bool: 1
+// CHECK:bool: 1
+// CHECK:bool: 1
+// CHECK:bool: 1
+// CHECK:string: 1
+// CHECK:string: 1
+// CHECK:string: 1
+// CHECK:string: 1
+// CHECK:string: 1
+// CHECK:string: 1
+// CHECK:string: 1
+// CHECK:string: 1
+// CHECK:int: 1
+// CHECK:int: 1
+// CHECK:int: 1
+// CHECK:int: 1
+// CHECK:int: 1
+// CHECK:int: 1
+// CHECK:int: 1
+// CHECK:int: 1
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/comparison/custom_equality.carbon b/explorer/testdata/comparison/custom_equality.carbon
index d243a8dab55c..558974d76be7 100644
--- a/explorer/testdata/comparison/custom_equality.carbon
+++ b/explorer/testdata/comparison/custom_equality.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: structs equal: 0
-// CHECK: structs not equal: 1
-// CHECK: result: 0
+// CHECK:structs equal: 0
+// CHECK:structs not equal: 1
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/comparison/fail_empty_struct.carbon b/explorer/testdata/comparison/fail_empty_struct.carbon
index d09a2b189dfb..b7a71614724b 100644
--- a/explorer/testdata/comparison/fail_empty_struct.carbon
+++ b/explorer/testdata/comparison/fail_empty_struct.carbon
@@ -2,13 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 2>&1 | %{FileCheck} %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 // TODO: This should work
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/comparison/fail_empty_struct.carbon:[[@LINE+1]]: type error in call: '{}' is not implicitly convertible to 'Type'
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/comparison/fail_empty_struct.carbon:[[@LINE+1]]: type error in call: '{}' is not implicitly convertible to 'Type'
 external impl {} as EqWith({}) {
   fn Equal[me: Self](other: Self) -> bool {
     return true;
diff --git a/explorer/testdata/comparison/fail_no_impl.carbon b/explorer/testdata/comparison/fail_no_impl.carbon
index 3a52076ddbce..01d51ee48c2c 100644
--- a/explorer/testdata/comparison/fail_no_impl.carbon
+++ b/explorer/testdata/comparison/fail_no_impl.carbon
@@ -2,13 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 2>&1 | %{FileCheck} %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/comparison/fail_no_impl.carbon:[[@LINE+1]]: i32 is not equality comparable with String (could not find implementation of interface EqWith(U = String) for i32)
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/comparison/fail_no_impl.carbon:[[@LINE+1]]: i32 is not equality comparable with String (could not find implementation of interface EqWith(U = String) for i32)
   Print("different types equal: {0}", if 1 == "1" then 1 else 0);
   return 0;
 }
diff --git a/explorer/testdata/constraint/binding_self.carbon b/explorer/testdata/constraint/binding_self.carbon
index 3ef0e6c2040c..216c84933899 100644
--- a/explorer/testdata/constraint/binding_self.carbon
+++ b/explorer/testdata/constraint/binding_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 12
+// CHECK:result: 12
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/constraint/combined_interfaces.carbon b/explorer/testdata/constraint/combined_interfaces.carbon
index b044544e769c..934a2d8f6b14 100644
--- a/explorer/testdata/constraint/combined_interfaces.carbon
+++ b/explorer/testdata/constraint/combined_interfaces.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 526
+// CHECK:result: 526
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/constraint/dot_self_is_other.carbon b/explorer/testdata/constraint/dot_self_is_other.carbon
index 6bee40ffa8a7..9506314c4337 100644
--- a/explorer/testdata/constraint/dot_self_is_other.carbon
+++ b/explorer/testdata/constraint/dot_self_is_other.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 12
+// CHECK:result: 12
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/constraint/fail_ambiguous_member.carbon b/explorer/testdata/constraint/fail_ambiguous_member.carbon
index 33ecde91c2ff..99af5bcbdbbb 100644
--- a/explorer/testdata/constraint/fail_ambiguous_member.carbon
+++ b/explorer/testdata/constraint/fail_ambiguous_member.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 interface A { fn F() -> i32; }
 interface B { fn F() -> i32; }
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_ambiguous_member.carbon:[[@LINE+1]]: ambiguous member access, F found in interface A and interface B
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_ambiguous_member.carbon:[[@LINE+1]]: ambiguous member access, F found in interface A and interface B
 fn Get[T:! A & B](n: T) -> i32 { return n.F(); }
 
 impl i32 as A {
diff --git a/explorer/testdata/constraint/fail_dot_self_after_scope.carbon b/explorer/testdata/constraint/fail_dot_self_after_scope.carbon
index dcf15c7db576..12acb7eda8fe 100644
--- a/explorer/testdata/constraint/fail_dot_self_after_scope.carbon
+++ b/explorer/testdata/constraint/fail_dot_self_after_scope.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 interface FrobWith(T:! Type) {}
 
 fn F[T:! FrobWith(.Self)]
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_dot_self_after_scope.carbon:[[@LINE+1]]: could not resolve '.Self'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_dot_self_after_scope.carbon:[[@LINE+1]]: could not resolve '.Self'
   (U: .Self) {
 }
 
diff --git a/explorer/testdata/constraint/fail_dot_self_after_scope_2.carbon b/explorer/testdata/constraint/fail_dot_self_after_scope_2.carbon
index c586f9609f70..5532df470e91 100644
--- a/explorer/testdata/constraint/fail_dot_self_after_scope_2.carbon
+++ b/explorer/testdata/constraint/fail_dot_self_after_scope_2.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 interface FrobWith(T:! Type) {}
 
 fn F[T:! FrobWith(.Self),
-     // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_dot_self_after_scope_2.carbon:[[@LINE+1]]: `.Self` used in type of non-type binding `U`
+     // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_dot_self_after_scope_2.carbon:[[@LINE+1]]: `.Self` used in type of non-type binding `U`
      U:! .Self]() {
 }
 
diff --git a/explorer/testdata/constraint/fail_dot_self_not_in_scope.carbon b/explorer/testdata/constraint/fail_dot_self_not_in_scope.carbon
index d7a9684ad702..ddee0b30257f 100644
--- a/explorer/testdata/constraint/fail_dot_self_not_in_scope.carbon
+++ b/explorer/testdata/constraint/fail_dot_self_not_in_scope.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_dot_self_not_in_scope.carbon:[[@LINE+1]]: could not resolve '.Self'
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_dot_self_not_in_scope.carbon:[[@LINE+1]]: could not resolve '.Self'
 fn Main() -> .Self {
   return 0;
 }
diff --git a/explorer/testdata/constraint/fail_infinite_self.carbon b/explorer/testdata/constraint/fail_infinite_self.carbon
index d9de04374912..cb517b5c9a7a 100644
--- a/explorer/testdata/constraint/fail_infinite_self.carbon
+++ b/explorer/testdata/constraint/fail_infinite_self.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_infinite_self.carbon:[[@LINE+1]]: `.Self` used in type of non-type binding `T`
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_infinite_self.carbon:[[@LINE+1]]: `.Self` used in type of non-type binding `T`
 fn F[T:! .Self]() {}
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/fail_infinite_self_ptr.carbon b/explorer/testdata/constraint/fail_infinite_self_ptr.carbon
index efa75f1d6a84..b35ca237fce7 100644
--- a/explorer/testdata/constraint/fail_infinite_self_ptr.carbon
+++ b/explorer/testdata/constraint/fail_infinite_self_ptr.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_infinite_self_ptr.carbon:[[@LINE+1]]: `.Self` used in type of non-type binding `T`
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_infinite_self_ptr.carbon:[[@LINE+1]]: `.Self` used in type of non-type binding `T`
 fn F[T:! .Self*]() {}
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/fail_non_type_self.carbon b/explorer/testdata/constraint/fail_non_type_self.carbon
index 56f8ef358696..f2d9b678159d 100644
--- a/explorer/testdata/constraint/fail_non_type_self.carbon
+++ b/explorer/testdata/constraint/fail_non_type_self.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 class X(T:! Type) {}
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_non_type_self.carbon:[[@LINE+1]]: `.Self` used in type of non-type binding `T`
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_non_type_self.carbon:[[@LINE+1]]: `.Self` used in type of non-type binding `T`
 fn F[T:! X(.Self)](x: T) {}
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/fail_where_equals_different_types.carbon b/explorer/testdata/constraint/fail_where_equals_different_types.carbon
index d8257a1e33dd..e6f6ef07d503 100644
--- a/explorer/testdata/constraint/fail_where_equals_different_types.carbon
+++ b/explorer/testdata/constraint/fail_where_equals_different_types.carbon
@@ -2,19 +2,17 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 interface A {}
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_where_equals_different_types.carbon:[[@LINE+3]]: type mismatch between values in `where LHS == RHS`
-// CHECK:   LHS type: i32
-// CHECK:   RHS type: Type
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_where_equals_different_types.carbon:[[@LINE+3]]: type mismatch between values in `where LHS == RHS`
+// CHECK:  LHS type: i32
+// CHECK:  RHS type: Type
 alias B = A where 4 == i32;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/fail_where_is_non_constraint.carbon b/explorer/testdata/constraint/fail_where_is_non_constraint.carbon
index 76421268eb85..0261b91a3a05 100644
--- a/explorer/testdata/constraint/fail_where_is_non_constraint.carbon
+++ b/explorer/testdata/constraint/fail_where_is_non_constraint.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 interface A {}
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_where_is_non_constraint.carbon:[[@LINE+1]]: expression after `is` does not resolve to a constraint, found value i32 of type Type
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_where_is_non_constraint.carbon:[[@LINE+1]]: expression after `is` does not resolve to a constraint, found value i32 of type Type
 alias B = A where i32 is i32;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/fail_where_is_non_type.carbon b/explorer/testdata/constraint/fail_where_is_non_type.carbon
index f20429429078..d1304d6b9500 100644
--- a/explorer/testdata/constraint/fail_where_is_non_type.carbon
+++ b/explorer/testdata/constraint/fail_where_is_non_type.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 interface A {}
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_where_is_non_type.carbon:[[@LINE+1]]: expression after `is` does not resolve to a constraint, found i32
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_where_is_non_type.carbon:[[@LINE+1]]: expression after `is` does not resolve to a constraint, found i32
 alias B = A where i32 is 5;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/fail_where_non_type_is.carbon b/explorer/testdata/constraint/fail_where_non_type_is.carbon
index a132a7276c60..4c0cdd599e4b 100644
--- a/explorer/testdata/constraint/fail_where_non_type_is.carbon
+++ b/explorer/testdata/constraint/fail_where_non_type_is.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 interface A {}
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_where_non_type_is.carbon:[[@LINE+1]]: Expected a type, but got 4
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/fail_where_non_type_is.carbon:[[@LINE+1]]: Expected a type, but got 4
 alias B = A where 4 is A;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/missing_member.carbon b/explorer/testdata/constraint/missing_member.carbon
index f8dda156cd10..96ca63b9d918 100644
--- a/explorer/testdata/constraint/missing_member.carbon
+++ b/explorer/testdata/constraint/missing_member.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 interface A { fn F() -> i32; }
 interface B { fn G() -> i32; }
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/missing_member.carbon:[[@LINE+1]]: member access, H not in constraint interface A & interface B where .Self:! Type is interface A and .Self:! Type is interface B
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/missing_member.carbon:[[@LINE+1]]: member access, H not in constraint interface A & interface B where .Self:! Type is interface A and .Self:! Type is interface B
 fn Get[T:! A & B](n: T) -> i32 { return n.H(); }
 
 impl i32 as A {
diff --git a/explorer/testdata/constraint/no_combine_equality.carbon b/explorer/testdata/constraint/no_combine_equality.carbon
index 7ff785ec031d..023d4f46e280 100644
--- a/explorer/testdata/constraint/no_combine_equality.carbon
+++ b/explorer/testdata/constraint/no_combine_equality.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,7 +13,7 @@ impl i32 as I {}
 
 fn F(A:! i32, B:! i32, C:! i32, D:! i32, E:! i32,
      T:! I where A == B and C == D and C == E and B == D) {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/no_combine_equality.carbon:[[@LINE+1]]: member access, F not in constraint interface I where .Self:! I is interface I and A:! i32 == B:! i32 and C:! i32 == D:! i32 and C:! i32 == E:! i32 and B:! i32 == D:! i32
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/constraint/no_combine_equality.carbon:[[@LINE+1]]: member access, F not in constraint interface I where .Self:! I is interface I and A:! i32 == B:! i32 and C:! i32 == D:! i32 and C:! i32 == E:! i32 and B:! i32 == D:! i32
   T.F();
 }
 
diff --git a/explorer/testdata/constraint/nondependent_where.carbon b/explorer/testdata/constraint/nondependent_where.carbon
index b151286415b0..b5d9aa23efe0 100644
--- a/explorer/testdata/constraint/nondependent_where.carbon
+++ b/explorer/testdata/constraint/nondependent_where.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/constraint/qualified_lookup_in_where.carbon b/explorer/testdata/constraint/qualified_lookup_in_where.carbon
index 04460eaa7cf6..cd51301b3ab6 100644
--- a/explorer/testdata/constraint/qualified_lookup_in_where.carbon
+++ b/explorer/testdata/constraint/qualified_lookup_in_where.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 122
+// CHECK:result: 122
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/constraint/where_self.carbon b/explorer/testdata/constraint/where_self.carbon
index 3abf0d78ef6c..467626603b5b 100644
--- a/explorer/testdata/constraint/where_self.carbon
+++ b/explorer/testdata/constraint/where_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 12
+// CHECK:result: 12
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/destructor/call_destructor_from_destructor.carbon b/explorer/testdata/destructor/call_destructor_from_destructor.carbon
index 5d0c792183a9..93df6b9bd692 100644
--- a/explorer/testdata/destructor/call_destructor_from_destructor.carbon
+++ b/explorer/testdata/destructor/call_destructor_from_destructor.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: DESTRUCTOR A 1
-// CHECK: DESTRUCTOR B 2
-// CHECK: DESTRUCTOR A 3
-// CHECK: DESTRUCTOR A 4
-// CHECK: result: 1
+// CHECK:DESTRUCTOR A 1
+// CHECK:DESTRUCTOR B 2
+// CHECK:DESTRUCTOR A 3
+// CHECK:DESTRUCTOR A 4
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/destructor/destructor_with_return.carbon b/explorer/testdata/destructor/destructor_with_return.carbon
index 1f04732b0ace..93d85a61931c 100644
--- a/explorer/testdata/destructor/destructor_with_return.carbon
+++ b/explorer/testdata/destructor/destructor_with_return.carbon
@@ -2,13 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: DESTRUCTOR A 3
-// CHECK: result: 1
+// CHECK:DESTRUCTOR A 3
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon b/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon
index 74aa50c7a256..444866d95c07 100644
--- a/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon
+++ b/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon
@@ -2,7 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 2>&1 | %{FileCheck} %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +14,7 @@ class A{
     }
     destructor[me: Self]{
         Print("DESTRUCTOR A2 {0}",me.n);
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon:[[@LINE+1]]: Duplicate name `destructor` also found at {{.*}}/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon:13
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon:[[@LINE+1]]: Duplicate name `destructor` also found at {{.*}}/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon:14
     }
     var n: i32;
 }
diff --git a/explorer/testdata/destructor/function_with_return.carbon b/explorer/testdata/destructor/function_with_return.carbon
index 66bdaa503ec0..7c0767faf620 100644
--- a/explorer/testdata/destructor/function_with_return.carbon
+++ b/explorer/testdata/destructor/function_with_return.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: DESTRUCTOR C 1
-// CHECK: DESTRUCTOR B 2
-// CHECK: DESTRUCTOR A 3
-// CHECK: result: 1
+// CHECK:DESTRUCTOR C 1
+// CHECK:DESTRUCTOR B 2
+// CHECK:DESTRUCTOR A 3
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/destructor/loop_block.carbon b/explorer/testdata/destructor/loop_block.carbon
index bfa3193fce9b..0d2534d7830d 100644
--- a/explorer/testdata/destructor/loop_block.carbon
+++ b/explorer/testdata/destructor/loop_block.carbon
@@ -2,18 +2,16 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: DESTRUCTOR A 1
-// CHECK: DESTRUCTOR A 2
-// CHECK: DESTRUCTOR A 3
-// CHECK: DESTRUCTOR A 1
-// CHECK: DESTRUCTOR A 2
-// CHECK: DESTRUCTOR A 3
-// CHECK: result: 1
+// CHECK:DESTRUCTOR A 1
+// CHECK:DESTRUCTOR A 2
+// CHECK:DESTRUCTOR A 3
+// CHECK:DESTRUCTOR A 1
+// CHECK:DESTRUCTOR A 2
+// CHECK:DESTRUCTOR A 3
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/destructor/loop_break_continue.carbon b/explorer/testdata/destructor/loop_break_continue.carbon
index f76b17ec6c25..7b6dddad6ead 100644
--- a/explorer/testdata/destructor/loop_break_continue.carbon
+++ b/explorer/testdata/destructor/loop_break_continue.carbon
@@ -2,23 +2,21 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: DESTRUCTOR A 1
-// CHECK: DESTRUCTOR A 2
-// CHECK: DESTRUCTOR A 3
-// CHECK: DESTRUCTOR A 4
-// CHECK: DESTRUCTOR A 5
-// CHECK: DESTRUCTOR A 6
-// CHECK: DESTRUCTOR A 7
-// CHECK: DESTRUCTOR A 8
-// CHECK: DESTRUCTOR A 6
-// CHECK: DESTRUCTOR A 7
-// CHECK: DESTRUCTOR A 8
-// CHECK: result: 1
+// CHECK:DESTRUCTOR A 1
+// CHECK:DESTRUCTOR A 2
+// CHECK:DESTRUCTOR A 3
+// CHECK:DESTRUCTOR A 4
+// CHECK:DESTRUCTOR A 5
+// CHECK:DESTRUCTOR A 6
+// CHECK:DESTRUCTOR A 7
+// CHECK:DESTRUCTOR A 8
+// CHECK:DESTRUCTOR A 6
+// CHECK:DESTRUCTOR A 7
+// CHECK:DESTRUCTOR A 8
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/destructor/nested_block_with_return.carbon b/explorer/testdata/destructor/nested_block_with_return.carbon
index e5ffa2d68d10..fe4bcf7370f8 100644
--- a/explorer/testdata/destructor/nested_block_with_return.carbon
+++ b/explorer/testdata/destructor/nested_block_with_return.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: DESTRUCTOR A 1
-// CHECK: DESTRUCTOR A 2
-// CHECK: DESTRUCTOR A 3
-// CHECK: DESTRUCTOR A 4
-// CHECK: result: 2
+// CHECK:DESTRUCTOR A 1
+// CHECK:DESTRUCTOR A 2
+// CHECK:DESTRUCTOR A 3
+// CHECK:DESTRUCTOR A 4
+// CHECK:result: 2
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/experimental_continuation/await_maintains_scope.carbon b/explorer/testdata/experimental_continuation/await_maintains_scope.carbon
index e643268b1f20..c7567a910536 100644
--- a/explorer/testdata/experimental_continuation/await_maintains_scope.carbon
+++ b/explorer/testdata/experimental_continuation/await_maintains_scope.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/experimental_continuation/convert_run.carbon b/explorer/testdata/experimental_continuation/convert_run.carbon
index c3a08f2c9fec..ff45f9516544 100644
--- a/explorer/testdata/experimental_continuation/convert_run.carbon
+++ b/explorer/testdata/experimental_continuation/convert_run.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/experimental_continuation/creation_is_noop.carbon b/explorer/testdata/experimental_continuation/creation_is_noop.carbon
index 6ef28af2af34..ba8e89c7a5f2 100644
--- a/explorer/testdata/experimental_continuation/creation_is_noop.carbon
+++ b/explorer/testdata/experimental_continuation/creation_is_noop.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/experimental_continuation/fail_auto_return_await.carbon b/explorer/testdata/experimental_continuation/fail_auto_return_await.carbon
index ba8c07515646..56a5a2153ad0 100644
--- a/explorer/testdata/experimental_continuation/fail_auto_return_await.carbon
+++ b/explorer/testdata/experimental_continuation/fail_auto_return_await.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn f() -> auto {
-   // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_auto_return_await.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
+   // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_auto_return_await.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
    __await;
 }
 
diff --git a/explorer/testdata/experimental_continuation/fail_continuation_syntax.carbon b/explorer/testdata/experimental_continuation/fail_continuation_syntax.carbon
index edc3985c8797..9d14d5160993 100644
--- a/explorer/testdata/experimental_continuation/fail_continuation_syntax.carbon
+++ b/explorer/testdata/experimental_continuation/fail_continuation_syntax.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32 = 0;
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_continuation_syntax.carbon:[[@LINE+1]]: syntax error, unexpected identifier, expecting LEFT_CURLY_BRACE
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_continuation_syntax.carbon:[[@LINE+1]]: syntax error, unexpected identifier, expecting LEFT_CURLY_BRACE
   __continuation k x = 3;
   __run k;
   return x;
diff --git a/explorer/testdata/experimental_continuation/fail_lifetime.carbon b/explorer/testdata/experimental_continuation/fail_lifetime.carbon
index ac9961ab2f94..0f95d2546bcb 100644
--- a/explorer/testdata/experimental_continuation/fail_lifetime.carbon
+++ b/explorer/testdata/experimental_continuation/fail_lifetime.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -17,7 +15,7 @@ package ExplorerTest api;
 fn capture() -> __Continuation {
   var x: i32 = 1;
   __continuation k {
-    // CHECK: RUNTIME ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_lifetime.carbon:[[@LINE+1]]: undefined behavior: access to dead value 1
+    // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_lifetime.carbon:[[@LINE+1]]: undefined behavior: access to dead value 1
     var y: i32 = x;
   }
   return k;
diff --git a/explorer/testdata/experimental_continuation/fail_recursive_continuation.carbon b/explorer/testdata/experimental_continuation/fail_recursive_continuation.carbon
index c53d5c769885..f793108f6215 100644
--- a/explorer/testdata/experimental_continuation/fail_recursive_continuation.carbon
+++ b/explorer/testdata/experimental_continuation/fail_recursive_continuation.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn f() {
   __continuation k {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_recursive_continuation.carbon:[[@LINE+1]]: 'k' is not usable until after it has been completely declared
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_recursive_continuation.carbon:[[@LINE+1]]: 'k' is not usable until after it has been completely declared
   __run k;
   }
 }
diff --git a/explorer/testdata/experimental_continuation/fail_return_in_continuation.carbon b/explorer/testdata/experimental_continuation/fail_return_in_continuation.carbon
index 36119c62fb6c..92e4cfdd37ed 100644
--- a/explorer/testdata/experimental_continuation/fail_return_in_continuation.carbon
+++ b/explorer/testdata/experimental_continuation/fail_return_in_continuation.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +12,7 @@ fn Main() -> i32 {
   var x: i32 = 0;
   __continuation k {
     x = x + 1;
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_return_in_continuation.carbon:[[@LINE+1]]: return is not within a function body
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/experimental_continuation/fail_return_in_continuation.carbon:[[@LINE+1]]: return is not within a function body
     return x;
   }
 }
diff --git a/explorer/testdata/experimental_continuation/recursive.carbon b/explorer/testdata/experimental_continuation/recursive.carbon
index 630a60c6339c..acfec0867b9f 100644
--- a/explorer/testdata/experimental_continuation/recursive.carbon
+++ b/explorer/testdata/experimental_continuation/recursive.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 10
+// CHECK:result: 10
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/experimental_continuation/run.carbon b/explorer/testdata/experimental_continuation/run.carbon
index f0eda1f87530..dcd4bf559da5 100644
--- a/explorer/testdata/experimental_continuation/run.carbon
+++ b/explorer/testdata/experimental_continuation/run.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/experimental_continuation/run_with_await.carbon b/explorer/testdata/experimental_continuation/run_with_await.carbon
index 432bc60577a8..b2b01b27ca12 100644
--- a/explorer/testdata/experimental_continuation/run_with_await.carbon
+++ b/explorer/testdata/experimental_continuation/run_with_await.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/experimental_continuation/shallow_copy.carbon b/explorer/testdata/experimental_continuation/shallow_copy.carbon
index 8383bba399ec..24ac6d4bee9e 100644
--- a/explorer/testdata/experimental_continuation/shallow_copy.carbon
+++ b/explorer/testdata/experimental_continuation/shallow_copy.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/for/for_loop.carbon b/explorer/testdata/for/for_loop.carbon
index 657215b46298..0ca88473f6af 100644
--- a/explorer/testdata/for/for_loop.carbon
+++ b/explorer/testdata/for/for_loop.carbon
@@ -2,36 +2,31 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: result: 8
+// CHECK:HALLO WELT 0
+// CHECK:HALLO WELT 1
+// CHECK:HALLO WELT 2
+// CHECK:HALLO WELT 3
+// CHECK:HALLO WELT 0
+// CHECK:HALLO WELT 1
+// CHECK:HALLO WELT 2
+// CHECK:HALLO WELT 3
+// CHECK:result: 8
 
 package ExplorerTest api;
 
-
-
-
 fn Main() -> i32 {
-  var ar: [i32; 4] = (0, 1,2,3);
-  var count : i32 = 0;
-  for( x: i32 in ar){
-      Print("HALLO WELT ", x);
-      count = count +1;
+  var ar: [i32; 4] = (0, 1, 2, 3);
+  var count: i32 = 0;
+  for (x: i32 in ar) {
+    Print("HALLO WELT {0}", x);
+    count = count + 1;
   }
-  for( x: i32 in ar){
-      Print("HALLO WELT ", x);
-      count = count +1;
+  for (x: i32 in ar) {
+    Print("HALLO WELT {0}", x);
+    count = count + 1;
   }
   return count;
 }
diff --git a/explorer/testdata/for/for_loop_auto.carbon b/explorer/testdata/for/for_loop_auto.carbon
index 2b19b78cf439..dfe7ddfc9a67 100644
--- a/explorer/testdata/for/for_loop_auto.carbon
+++ b/explorer/testdata/for/for_loop_auto.carbon
@@ -2,28 +2,23 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: HALLO WELT
-// CHECK: result: 4
+// CHECK:HALLO WELT 0
+// CHECK:HALLO WELT 1
+// CHECK:HALLO WELT 2
+// CHECK:HALLO WELT 3
+// CHECK:result: 4
 
 package ExplorerTest api;
 
-
-
-
 fn Main() -> i32 {
-  var ar: [i32; 4] = (0, 1,2,3);
-  var count : i32 = 0;
-  for( x: auto in ar){
-      Print("HALLO WELT ", x);
-      count = count +1;
+  var ar: [i32; 4] = (0, 1, 2, 3);
+  var count: i32 = 0;
+  for (x: auto in ar) {
+    Print("HALLO WELT {0}", x);
+    count = count + 1;
   }
   return count;
 }
diff --git a/explorer/testdata/for/for_loop_break.carbon b/explorer/testdata/for/for_loop_break.carbon
index b6d1e1311349..d1011ea90cec 100644
--- a/explorer/testdata/for/for_loop_break.carbon
+++ b/explorer/testdata/for/for_loop_break.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/for/for_loop_continue.carbon b/explorer/testdata/for/for_loop_continue.carbon
index d4720d7ce494..4936a3784f43 100644
--- a/explorer/testdata/for/for_loop_continue.carbon
+++ b/explorer/testdata/for/for_loop_continue.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 4
+// CHECK:result: 4
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/for/for_loop_empty.carbon b/explorer/testdata/for/for_loop_empty.carbon
index 781be8909897..1eeeeeb2ef1c 100644
--- a/explorer/testdata/for/for_loop_empty.carbon
+++ b/explorer/testdata/for/for_loop_empty.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/for/for_loop_nested.carbon b/explorer/testdata/for/for_loop_nested.carbon
index ce1d381c52ec..f000e39803f7 100644
--- a/explorer/testdata/for/for_loop_nested.carbon
+++ b/explorer/testdata/for/for_loop_nested.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 20
+// CHECK:result: 20
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/auto_return/add.carbon b/explorer/testdata/function/auto_return/add.carbon
index 7eec2391c41d..1c4b1aae0140 100644
--- a/explorer/testdata/function/auto_return/add.carbon
+++ b/explorer/testdata/function/auto_return/add.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/auto_return/fail_direct_recurse.carbon b/explorer/testdata/function/auto_return/fail_direct_recurse.carbon
index f2805ed32460..4af82fb2c6b6 100644
--- a/explorer/testdata/function/auto_return/fail_direct_recurse.carbon
+++ b/explorer/testdata/function/auto_return/fail_direct_recurse.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +12,7 @@ package ExplorerTest api;
 // used.
 fn Recurse(x: i32, do_recurse: bool) -> auto {
   if (do_recurse) {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/auto_return/fail_direct_recurse.carbon:[[@LINE+1]]: Function calls itself, but has a deduced return type
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/auto_return/fail_direct_recurse.carbon:[[@LINE+1]]: Function calls itself, but has a deduced return type
     Recurse(x, false);
   }
   return x;
diff --git a/explorer/testdata/function/auto_return/fail_multiple_returns.carbon b/explorer/testdata/function/auto_return/fail_multiple_returns.carbon
index e83d30c50c17..7c01e564701c 100644
--- a/explorer/testdata/function/auto_return/fail_multiple_returns.carbon
+++ b/explorer/testdata/function/auto_return/fail_multiple_returns.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +12,7 @@ fn Add(x: i32, y: i32) -> auto {
   if (x == 0) {
     return x;
   } else if (y == 0) {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/auto_return/fail_multiple_returns.carbon:[[@LINE+1]]: Only one return is allowed in a function with an `auto` return type.
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/auto_return/fail_multiple_returns.carbon:[[@LINE+1]]: Only one return is allowed in a function with an `auto` return type.
     return y;
   } else {
     return x + y;
diff --git a/explorer/testdata/function/auto_return/fail_no_return.carbon b/explorer/testdata/function/auto_return/fail_no_return.carbon
index 9fb3a6721833..76c67a86ff16 100644
--- a/explorer/testdata/function/auto_return/fail_no_return.carbon
+++ b/explorer/testdata/function/auto_return/fail_no_return.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn NoReturn() -> auto {
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/auto_return/fail_no_return.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/auto_return/fail_no_return.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
 }
 
 fn Main() {
diff --git a/explorer/testdata/function/auto_return/fail_separate_decl.carbon b/explorer/testdata/function/auto_return/fail_separate_decl.carbon
index e23d42a98083..77b22af1efa2 100644
--- a/explorer/testdata/function/auto_return/fail_separate_decl.carbon
+++ b/explorer/testdata/function/auto_return/fail_separate_decl.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 // This declaration is not allowed.
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/auto_return/fail_separate_decl.carbon:[[@LINE+1]]: Function declaration has deduced return type but no body
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/auto_return/fail_separate_decl.carbon:[[@LINE+1]]: Function declaration has deduced return type but no body
 fn Add(x: i32, y: i32) -> auto;
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/function/auto_return/modify_arg_type.carbon b/explorer/testdata/function/auto_return/modify_arg_type.carbon
index 71add53cea84..4f9cdb9e4867 100644
--- a/explorer/testdata/function/auto_return/modify_arg_type.carbon
+++ b/explorer/testdata/function/auto_return/modify_arg_type.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/auto_return/modify_return_type.carbon b/explorer/testdata/function/auto_return/modify_return_type.carbon
index 8d01bc3e114d..05d26c5de5c8 100644
--- a/explorer/testdata/function/auto_return/modify_return_type.carbon
+++ b/explorer/testdata/function/auto_return/modify_return_type.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/auto_return/type.carbon b/explorer/testdata/function/auto_return/type.carbon
index 7477746b4f96..d0d4c9a04287 100644
--- a/explorer/testdata/function/auto_return/type.carbon
+++ b/explorer/testdata/function/auto_return/type.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/convert_args.carbon b/explorer/testdata/function/convert_args.carbon
index 9b094843edfb..342746cd22ff 100644
--- a/explorer/testdata/function/convert_args.carbon
+++ b/explorer/testdata/function/convert_args.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 123
+// CHECK:result: 123
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/empty_params.carbon b/explorer/testdata/function/empty_params.carbon
index a8362e9427be..79cfa9a30fec 100644
--- a/explorer/testdata/function/empty_params.carbon
+++ b/explorer/testdata/function/empty_params.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/fail_call_with_tuple.carbon b/explorer/testdata/function/fail_call_with_tuple.carbon
index 23e8737c7423..263ac56f35e5 100644
--- a/explorer/testdata/function/fail_call_with_tuple.carbon
+++ b/explorer/testdata/function/fail_call_with_tuple.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,6 +13,6 @@ fn f(x: i32, y: i32) -> i32 { return x + y; }
 fn Main() -> i32 {
   var xy: (i32, i32) = (1, 2);
   // should fail to type-check
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_call_with_tuple.carbon:[[@LINE+1]]: wrong number of arguments in function call, expected 2 but got 1
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_call_with_tuple.carbon:[[@LINE+1]]: wrong number of arguments in function call, expected 2 but got 1
   return f(xy);
 }
diff --git a/explorer/testdata/function/fail_invalid_fnty.carbon b/explorer/testdata/function/fail_invalid_fnty.carbon
index 77642b7d3389..65c2801fa316 100644
--- a/explorer/testdata/function/fail_invalid_fnty.carbon
+++ b/explorer/testdata/function/fail_invalid_fnty.carbon
@@ -2,18 +2,16 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 // TODO: We should type-check the prelude before the main input so that we can
 // use it within the types of top-level declarations.
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_invalid_fnty.carbon:[[@LINE+2]]: type error in `-`:
-// CHECK: missing declaration for builtin `Negate`
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_invalid_fnty.carbon:[[@LINE+2]]: type error in `-`:
+// CHECK:missing declaration for builtin `Negate`
 fn f(g: __Fn(-true) -> true) {
 }
 
diff --git a/explorer/testdata/function/fail_match_no_return.carbon b/explorer/testdata/function/fail_match_no_return.carbon
index b16e52a6e82c..d481d36458ef 100644
--- a/explorer/testdata/function/fail_match_no_return.carbon
+++ b/explorer/testdata/function/fail_match_no_return.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: i32 = 0;
   match(0) {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_match_no_return.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_match_no_return.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
     case 1 => { x = 1; }
     case _: auto => { x = 2; }
   }
diff --git a/explorer/testdata/function/fail_match_partial_return.carbon b/explorer/testdata/function/fail_match_partial_return.carbon
index 87aeacf7ce66..d67960293946 100644
--- a/explorer/testdata/function/fail_match_partial_return.carbon
+++ b/explorer/testdata/function/fail_match_partial_return.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: i32 = 0;
   match (0) {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_match_partial_return.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_match_partial_return.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
     case 1 => { x = 1; }
     case _: auto => { return 0; }
   }
diff --git a/explorer/testdata/function/fail_non_exhaustive_match.carbon b/explorer/testdata/function/fail_non_exhaustive_match.carbon
index 98d0a95cb851..8505f6f8ae35 100644
--- a/explorer/testdata/function/fail_non_exhaustive_match.carbon
+++ b/explorer/testdata/function/fail_non_exhaustive_match.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,5 +13,5 @@ fn Main() -> i32 {
   match (n) {
     case 1 => { return 0; }
   }
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_non_exhaustive_match.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_non_exhaustive_match.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
 }
diff --git a/explorer/testdata/function/fail_parameter_type.carbon b/explorer/testdata/function/fail_parameter_type.carbon
index 0d5f48c6260b..d99d659624fd 100644
--- a/explorer/testdata/function/fail_parameter_type.carbon
+++ b/explorer/testdata/function/fail_parameter_type.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 // 42 cannot be used as the type of a parameter.
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_parameter_type.carbon:[[@LINE+1]]: Expected a type, but got 42
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/function/fail_parameter_type.carbon:[[@LINE+1]]: Expected a type, but got 42
 fn f(x: 42) -> i32 {
   return x - 1;
 }
diff --git a/explorer/testdata/function/fnty.carbon b/explorer/testdata/function/fnty.carbon
index 11237cf40892..269b44251b2e 100644
--- a/explorer/testdata/function/fnty.carbon
+++ b/explorer/testdata/function/fnty.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/ignored_parameter.carbon b/explorer/testdata/function/ignored_parameter.carbon
index 599b745ff80d..97fe833fe7a3 100644
--- a/explorer/testdata/function/ignored_parameter.carbon
+++ b/explorer/testdata/function/ignored_parameter.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/multiple_args.carbon b/explorer/testdata/function/multiple_args.carbon
index fc9f580f3594..3cf664c64c63 100644
--- a/explorer/testdata/function/multiple_args.carbon
+++ b/explorer/testdata/function/multiple_args.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/non_exhaustive_match_no_return_type.carbon b/explorer/testdata/function/non_exhaustive_match_no_return_type.carbon
index 3d2440130947..bff7bb133819 100644
--- a/explorer/testdata/function/non_exhaustive_match_no_return_type.carbon
+++ b/explorer/testdata/function/non_exhaustive_match_no_return_type.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/non_exhaustive_match_return.carbon b/explorer/testdata/function/non_exhaustive_match_return.carbon
index 54c900b2e8c0..f55980ca48fa 100644
--- a/explorer/testdata/function/non_exhaustive_match_return.carbon
+++ b/explorer/testdata/function/non_exhaustive_match_return.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/param_lifetime.carbon b/explorer/testdata/function/param_lifetime.carbon
index 9f284df653b0..3de28786a3cc 100644
--- a/explorer/testdata/function/param_lifetime.carbon
+++ b/explorer/testdata/function/param_lifetime.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/recursive.carbon b/explorer/testdata/function/recursive.carbon
index b1d63a87ad53..55b7e11fd9da 100644
--- a/explorer/testdata/function/recursive.carbon
+++ b/explorer/testdata/function/recursive.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/return.carbon b/explorer/testdata/function/return.carbon
index cc2e0c6a98bc..8196b9497fd4 100644
--- a/explorer/testdata/function/return.carbon
+++ b/explorer/testdata/function/return.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/return_exhaustive_match.carbon b/explorer/testdata/function/return_exhaustive_match.carbon
index cacf2ba1721a..edcc82f08483 100644
--- a/explorer/testdata/function/return_exhaustive_match.carbon
+++ b/explorer/testdata/function/return_exhaustive_match.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/function/type_match.carbon b/explorer/testdata/function/type_match.carbon
index 28401b16a5c5..48fc382b2055 100644
--- a/explorer/testdata/function/type_match.carbon
+++ b/explorer/testdata/function/type_match.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/class_function.carbon b/explorer/testdata/generic_class/class_function.carbon
index 49017109bf7b..14acc5e4c5e8 100644
--- a/explorer/testdata/generic_class/class_function.carbon
+++ b/explorer/testdata/generic_class/class_function.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/convert_from_struct.carbon b/explorer/testdata/generic_class/convert_from_struct.carbon
index f0875a6bf853..828017ca7f22 100644
--- a/explorer/testdata/generic_class/convert_from_struct.carbon
+++ b/explorer/testdata/generic_class/convert_from_struct.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 5
+// CHECK:result: 5
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/fail_args_mismatch.carbon b/explorer/testdata/generic_class/fail_args_mismatch.carbon
index 62eca4c7ae75..6d7680f47fb8 100644
--- a/explorer/testdata/generic_class/fail_args_mismatch.carbon
+++ b/explorer/testdata/generic_class/fail_args_mismatch.carbon
@@ -2,15 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false --dump-input=always -v %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 class Point(T:! Type) {
   // Point(T, T) does not match class declaration
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_args_mismatch.carbon:[[@LINE+1]]: wrong number of arguments in function call, expected 1 but got 2
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_args_mismatch.carbon:[[@LINE+1]]: wrong number of arguments in function call, expected 1 but got 2
   fn Origin(zero: T) -> Point(T, T) {
     return {.x = zero, .y = zero};
   }
diff --git a/explorer/testdata/generic_class/fail_argument_deduction.carbon b/explorer/testdata/generic_class/fail_argument_deduction.carbon
index 5ad7276d4b52..5f6f7518fbc7 100644
--- a/explorer/testdata/generic_class/fail_argument_deduction.carbon
+++ b/explorer/testdata/generic_class/fail_argument_deduction.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -22,8 +20,8 @@ fn FirstOfTwoPoints[T:! Type](a: Point(T), b: Point(T)) -> Point(T) {
 fn Main() -> i32 {
   var p: Point(i32) = {.x = 0, .y = 1};
   var q: Point(bool) = {.x = true, .y = false};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_argument_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! Type:
-  // CHECK:   i32
-  // CHECK:   bool
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_argument_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! Type:
+  // CHECK:  i32
+  // CHECK:  bool
   return FirstOfTwoPoints(p, q).x;
 }
diff --git a/explorer/testdata/generic_class/fail_bad_parameter_type.carbon b/explorer/testdata/generic_class/fail_bad_parameter_type.carbon
index 03839182c87a..b0be30411e26 100644
--- a/explorer/testdata/generic_class/fail_bad_parameter_type.carbon
+++ b/explorer/testdata/generic_class/fail_bad_parameter_type.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -24,7 +22,7 @@ class Point(T:! i32) {
 }
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_bad_parameter_type.carbon:[[@LINE+1]]: type error in call: 'Type' is not implicitly convertible to 'i32'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_bad_parameter_type.carbon:[[@LINE+1]]: type error in call: 'Type' is not implicitly convertible to 'i32'
   var p: Point(i32) = Point(i32).Origin(0);
   return p.GetX();
 }
diff --git a/explorer/testdata/generic_class/fail_field_access_on_generic.carbon b/explorer/testdata/generic_class/fail_field_access_on_generic.carbon
index 5006628c9b67..751d3536e4ae 100644
--- a/explorer/testdata/generic_class/fail_field_access_on_generic.carbon
+++ b/explorer/testdata/generic_class/fail_field_access_on_generic.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn BadSimpleMemberAccess[T:! Type](a: T) -> T {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_field_access_on_generic.carbon:[[@LINE+1]]: member access in unconstrained type
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_field_access_on_generic.carbon:[[@LINE+1]]: member access in unconstrained type
   return a.x;
 }
 
diff --git a/explorer/testdata/generic_class/fail_generic_class_arg.carbon b/explorer/testdata/generic_class/fail_generic_class_arg.carbon
index bfd034b5b5f8..21526e81dc8c 100644
--- a/explorer/testdata/generic_class/fail_generic_class_arg.carbon
+++ b/explorer/testdata/generic_class/fail_generic_class_arg.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -20,7 +18,7 @@ class Point(T:! Type) {
 }
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_generic_class_arg.carbon:[[@LINE+1]]: wrong number of arguments in function call, expected 1 but got 2
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_generic_class_arg.carbon:[[@LINE+1]]: wrong number of arguments in function call, expected 1 but got 2
   var p: Point(i32) = Point(i32, i32).Create(0, 1);
   return p.x;
 }
diff --git a/explorer/testdata/generic_class/fail_generic_in_pattern.carbon b/explorer/testdata/generic_class/fail_generic_in_pattern.carbon
index 595e41c5619d..4545be5dd8ce 100644
--- a/explorer/testdata/generic_class/fail_generic_in_pattern.carbon
+++ b/explorer/testdata/generic_class/fail_generic_in_pattern.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var t: auto = 5;
   match (t) {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_generic_in_pattern.carbon:[[@LINE+1]]: Generic binding may not occur in pattern with expected type: T:! i32
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_generic_in_pattern.carbon:[[@LINE+1]]: Generic binding may not occur in pattern with expected type: T:! i32
     case T:! i32 => { return 0; }
     default => { return 1; }
   }
diff --git a/explorer/testdata/generic_class/fail_instantiate_non_generic.carbon b/explorer/testdata/generic_class/fail_instantiate_non_generic.carbon
index 9103911ccee1..0d5e78283ff2 100644
--- a/explorer/testdata/generic_class/fail_instantiate_non_generic.carbon
+++ b/explorer/testdata/generic_class/fail_instantiate_non_generic.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -19,7 +17,7 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_instantiate_non_generic.carbon:[[@LINE+1]]: in call `Point(i32)`, expected callee to be a function, found `typeof(class Point)`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_instantiate_non_generic.carbon:[[@LINE+1]]: in call `Point(i32)`, expected callee to be a function, found `typeof(class Point)`
   var p: Point(i32) = Point.Origin();
   return 0;
 }
diff --git a/explorer/testdata/generic_class/fail_no_args.carbon b/explorer/testdata/generic_class/fail_no_args.carbon
index b737d1c7ccdd..6114d833fc6f 100644
--- a/explorer/testdata/generic_class/fail_no_args.carbon
+++ b/explorer/testdata/generic_class/fail_no_args.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ class Point(T:! Type) {
   }
 
   // Error: wrote `Point` instead of `Point(T)`, `Point` by itself is not a type.
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_no_args.carbon:[[@LINE+1]]: Expected a type, but got Point
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_no_args.carbon:[[@LINE+1]]: Expected a type, but got Point
   fn GetX[me: Point]() -> T {
     return me.x;
   }
diff --git a/explorer/testdata/generic_class/fail_point_equal.carbon b/explorer/testdata/generic_class/fail_point_equal.carbon
index 442704d45813..0edf94acfae6 100644
--- a/explorer/testdata/generic_class/fail_point_equal.carbon
+++ b/explorer/testdata/generic_class/fail_point_equal.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -17,7 +15,7 @@ class Point(T:! Type) {
 
 fn Main() -> i32 {
   var p: Point(i32) = {.x = 0, .y = 0};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_point_equal.carbon:[[@LINE+1]]: type error in name binding: 'class Point(T = i32)' is not implicitly convertible to 'class Point(T = bool)'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_point_equal.carbon:[[@LINE+1]]: type error in name binding: 'class Point(T = i32)' is not implicitly convertible to 'class Point(T = bool)'
   var q: Point(bool) = p;
   return 0;
 }
diff --git a/explorer/testdata/generic_class/fail_return_type_is_type.carbon b/explorer/testdata/generic_class/fail_return_type_is_type.carbon
index 2f757dd2ea2c..f1e08c459d33 100644
--- a/explorer/testdata/generic_class/fail_return_type_is_type.carbon
+++ b/explorer/testdata/generic_class/fail_return_type_is_type.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 class Point(T:! Type) {
   // The return type should be Point(T). Point by itself is not a type.
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_return_type_is_type.carbon:[[@LINE+1]]: Expected a type, but got Point
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_return_type_is_type.carbon:[[@LINE+1]]: Expected a type, but got Point
   fn Create(x: T, y: T) -> Point {
     return {.x = x, .y = y};
   }
diff --git a/explorer/testdata/generic_class/fail_self_with_arg.carbon b/explorer/testdata/generic_class/fail_self_with_arg.carbon
index 44600e9081d6..82fd856e121b 100644
--- a/explorer/testdata/generic_class/fail_self_with_arg.carbon
+++ b/explorer/testdata/generic_class/fail_self_with_arg.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 class Point(T:! Type) {
 
   // Error: wrote `Self(T)` instead of `Self`.
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_self_with_arg.carbon:[[@LINE+1]]: in call `Self(T)`, expected callee to be a function, found `typeof(class Point(T = T:! Type))`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_self_with_arg.carbon:[[@LINE+1]]: in call `Self(T)`, expected callee to be a function, found `typeof(class Point(T = T:! Type))`
   fn Origin(zero: T) -> Self(T) {
     return {.x = zero, .y = zero};
   }
diff --git a/explorer/testdata/generic_class/fail_two_arg_lists.carbon b/explorer/testdata/generic_class/fail_two_arg_lists.carbon
index 262785406274..1cb9b2c69a79 100644
--- a/explorer/testdata/generic_class/fail_two_arg_lists.carbon
+++ b/explorer/testdata/generic_class/fail_two_arg_lists.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 class Point(T:! Type) {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_two_arg_lists.carbon:[[@LINE+1]]: in call `Point(T)(T)`, expected callee to be a function, found `typeof(class Point(T = T:! Type))`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_two_arg_lists.carbon:[[@LINE+1]]: in call `Point(T)(T)`, expected callee to be a function, found `typeof(class Point(T = T:! Type))`
   fn Origin(zero: T) -> Point(T)(T) {
     return {.x = zero, .y = zero};
   }
diff --git a/explorer/testdata/generic_class/fail_value_param_mismatch.carbon b/explorer/testdata/generic_class/fail_value_param_mismatch.carbon
index abcb43331d0c..6d8c7f5dc5f1 100644
--- a/explorer/testdata/generic_class/fail_value_param_mismatch.carbon
+++ b/explorer/testdata/generic_class/fail_value_param_mismatch.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ fn F(x: HasI32Param(1)) {}
 
 fn Main() -> i32 {
   var n: HasI32Param(0) = {};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_value_param_mismatch.carbon:[[@LINE+1]]: mismatch in non-type values, `0` != `1`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_class/fail_value_param_mismatch.carbon:[[@LINE+1]]: mismatch in non-type values, `0` != `1`
   F(n);
   return 0;
 }
diff --git a/explorer/testdata/generic_class/generic_class_substitution.carbon b/explorer/testdata/generic_class/generic_class_substitution.carbon
index bf22c5a61cc3..779d21b00af4 100644
--- a/explorer/testdata/generic_class/generic_class_substitution.carbon
+++ b/explorer/testdata/generic_class/generic_class_substitution.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/generic_fun_and_class.carbon b/explorer/testdata/generic_class/generic_fun_and_class.carbon
index f62ea7a54e2e..e0c1c4d55ef8 100644
--- a/explorer/testdata/generic_class/generic_fun_and_class.carbon
+++ b/explorer/testdata/generic_class/generic_fun_and_class.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/generic_point.carbon b/explorer/testdata/generic_class/generic_point.carbon
index 58d39d257aa6..5c18e6a0c007 100644
--- a/explorer/testdata/generic_class/generic_point.carbon
+++ b/explorer/testdata/generic_class/generic_point.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/impl_with_argument.carbon b/explorer/testdata/generic_class/impl_with_argument.carbon
index 6bef60e3ebb3..06b6b49d89dc 100644
--- a/explorer/testdata/generic_class/impl_with_argument.carbon
+++ b/explorer/testdata/generic_class/impl_with_argument.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/impl_with_self.carbon b/explorer/testdata/generic_class/impl_with_self.carbon
index edfa65b6e7cc..34ec8996ccec 100644
--- a/explorer/testdata/generic_class/impl_with_self.carbon
+++ b/explorer/testdata/generic_class/impl_with_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/instantiation_at_compile_time.carbon b/explorer/testdata/generic_class/instantiation_at_compile_time.carbon
index 0df9059adefc..b133d3c5ff01 100644
--- a/explorer/testdata/generic_class/instantiation_at_compile_time.carbon
+++ b/explorer/testdata/generic_class/instantiation_at_compile_time.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/param_with_dependent_type.carbon b/explorer/testdata/generic_class/param_with_dependent_type.carbon
index 12b1cab95ae4..1a7a4271aae7 100644
--- a/explorer/testdata/generic_class/param_with_dependent_type.carbon
+++ b/explorer/testdata/generic_class/param_with_dependent_type.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/point_with_interface.carbon b/explorer/testdata/generic_class/point_with_interface.carbon
index 948cda25954f..d9ad38df7486 100644
--- a/explorer/testdata/generic_class/point_with_interface.carbon
+++ b/explorer/testdata/generic_class/point_with_interface.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/use_at_compile_time.carbon b/explorer/testdata/generic_class/use_at_compile_time.carbon
index 6c268dc50daa..113bd83321b2 100644
--- a/explorer/testdata/generic_class/use_at_compile_time.carbon
+++ b/explorer/testdata/generic_class/use_at_compile_time.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_class/use_self.carbon b/explorer/testdata/generic_class/use_self.carbon
index 9f7544d59a25..a5459922fced 100644
--- a/explorer/testdata/generic_class/use_self.carbon
+++ b/explorer/testdata/generic_class/use_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_function/apply.carbon b/explorer/testdata/generic_function/apply.carbon
index 23adb60b3c55..c34f6256f3d2 100644
--- a/explorer/testdata/generic_function/apply.carbon
+++ b/explorer/testdata/generic_function/apply.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: -2
+// CHECK:result: -2
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_function/call_at_compile_time.carbon b/explorer/testdata/generic_function/call_at_compile_time.carbon
index 0ace774c63a9..d8558c870f99 100644
--- a/explorer/testdata/generic_function/call_at_compile_time.carbon
+++ b/explorer/testdata/generic_function/call_at_compile_time.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_function/fail_implicit_conversion_extra_field.carbon b/explorer/testdata/generic_function/fail_implicit_conversion_extra_field.carbon
index bd5c06765a0b..f59a4ca4de65 100644
--- a/explorer/testdata/generic_function/fail_implicit_conversion_extra_field.carbon
+++ b/explorer/testdata/generic_function/fail_implicit_conversion_extra_field.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn Bad[T:! Type](x: {.a: i32, .b: T}) {}
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_implicit_conversion_extra_field.carbon:[[@LINE+1]]: mismatch in field names, source field `c` not in destination type `{.a: i32, .b: T:! Type}`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_implicit_conversion_extra_field.carbon:[[@LINE+1]]: mismatch in field names, source field `c` not in destination type `{.a: i32, .b: T:! Type}`
   Bad({.b = 5, .a = 7, .c = 2});
   return 0;
 }
diff --git a/explorer/testdata/generic_function/fail_implicit_conversion_missing_field.carbon b/explorer/testdata/generic_function/fail_implicit_conversion_missing_field.carbon
index faaa3cdfa469..cb9dc04defa6 100644
--- a/explorer/testdata/generic_function/fail_implicit_conversion_missing_field.carbon
+++ b/explorer/testdata/generic_function/fail_implicit_conversion_missing_field.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn Bad[T:! Type](x: {.a: i32, .b: T}) {}
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_implicit_conversion_missing_field.carbon:[[@LINE+1]]: mismatch in field names, destination field `b` not in source type `{.a: i32}`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_implicit_conversion_missing_field.carbon:[[@LINE+1]]: mismatch in field names, destination field `b` not in source type `{.a: i32}`
   Bad({.a = 5});
   return 0;
 }
diff --git a/explorer/testdata/generic_function/fail_missing_exclam.carbon b/explorer/testdata/generic_function/fail_missing_exclam.carbon
index af13759f489a..28bf96da919c 100644
--- a/explorer/testdata/generic_function/fail_missing_exclam.carbon
+++ b/explorer/testdata/generic_function/fail_missing_exclam.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/generic_function/fail_missing_exclam.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
+// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/generic_function/fail_missing_exclam.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
 fn F[T: Type]();
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/generic_function/fail_not_addable.carbon b/explorer/testdata/generic_function/fail_not_addable.carbon
index 9576fc273222..492205f3513a 100644
--- a/explorer/testdata/generic_function/fail_not_addable.carbon
+++ b/explorer/testdata/generic_function/fail_not_addable.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn id[T:! Type](x: T) -> T {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_not_addable.carbon:[[@LINE+2]]: type error in `+`:
-  // CHECK: could not find implementation of interface AddWith(U = i32) for T:! Type
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_not_addable.carbon:[[@LINE+2]]: type error in `+`:
+  // CHECK:could not find implementation of interface AddWith(U = i32) for T:! Type
   return x + 0;
 }
 
diff --git a/explorer/testdata/generic_function/fail_not_type.carbon b/explorer/testdata/generic_function/fail_not_type.carbon
index c8058432f737..dc9d873a852e 100644
--- a/explorer/testdata/generic_function/fail_not_type.carbon
+++ b/explorer/testdata/generic_function/fail_not_type.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_not_type.carbon:[[@LINE+1]]: Expected a type, but got 42
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_not_type.carbon:[[@LINE+1]]: Expected a type, but got 42
 fn F[a:! 42]();
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/generic_function/fail_type_deduction_mismatch.carbon b/explorer/testdata/generic_function/fail_type_deduction_mismatch.carbon
index 95908dc0016c..0011131b61ed 100644
--- a/explorer/testdata/generic_function/fail_type_deduction_mismatch.carbon
+++ b/explorer/testdata/generic_function/fail_type_deduction_mismatch.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,8 +13,8 @@ fn fst[T:! Type](x: T, y: T) -> T {
 }
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_type_deduction_mismatch.carbon:[[@LINE+3]]: deduced multiple different values for T:! Type:
-  // CHECK:   i32
-  // CHECK:   bool
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_type_deduction_mismatch.carbon:[[@LINE+3]]: deduced multiple different values for T:! Type:
+  // CHECK:  i32
+  // CHECK:  bool
   return fst(0, true);
 }
diff --git a/explorer/testdata/generic_function/fail_type_deduction_unused.carbon b/explorer/testdata/generic_function/fail_type_deduction_unused.carbon
index 8de1b49bc8ce..5a6069b72e6d 100644
--- a/explorer/testdata/generic_function/fail_type_deduction_unused.carbon
+++ b/explorer/testdata/generic_function/fail_type_deduction_unused.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,7 +13,7 @@ fn id[T:! Type](x: i32) -> i32 {
 }
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_type_deduction_unused.carbon:[[@LINE+2]]: could not deduce type argument for type parameter T
-  // CHECK: in id(0)
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_type_deduction_unused.carbon:[[@LINE+2]]: could not deduce type argument for type parameter T
+  // CHECK:in id(0)
   return id(0);
 }
diff --git a/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon b/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon
index 169b9b4e4bd5..2988fd927f17 100644
--- a/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon
+++ b/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package Foo api;
@@ -17,7 +15,7 @@ fn Get[T:! ()](n: T) -> i32 {  return 2; }
 
 fn Main() -> i32 {
   var x : X = {};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon:[[@LINE+1]]: cannot convert deduced value class X for T to parameter type ()
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon:[[@LINE+1]]: cannot convert deduced value class X for T to parameter type ()
   Get(x);
   return 0;
 }
diff --git a/explorer/testdata/generic_function/generic_method.carbon b/explorer/testdata/generic_function/generic_method.carbon
index 42e90001cb3e..7b2356bcdd27 100644
--- a/explorer/testdata/generic_function/generic_method.carbon
+++ b/explorer/testdata/generic_function/generic_method.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_function/implicit_conversion.carbon b/explorer/testdata/generic_function/implicit_conversion.carbon
index ad6ee0025e8e..dabd9a026957 100644
--- a/explorer/testdata/generic_function/implicit_conversion.carbon
+++ b/explorer/testdata/generic_function/implicit_conversion.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 4213
+// CHECK:result: 4213
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_function/non_generic_param.carbon b/explorer/testdata/generic_function/non_generic_param.carbon
index 0c9ae63d3984..13f736142574 100644
--- a/explorer/testdata/generic_function/non_generic_param.carbon
+++ b/explorer/testdata/generic_function/non_generic_param.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_function/nondeduced_generic_param.carbon b/explorer/testdata/generic_function/nondeduced_generic_param.carbon
index d2e3b032b23b..88947c351e64 100644
--- a/explorer/testdata/generic_function/nondeduced_generic_param.carbon
+++ b/explorer/testdata/generic_function/nondeduced_generic_param.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 class A(T:! Type) {
diff --git a/explorer/testdata/generic_function/return_val.carbon b/explorer/testdata/generic_function/return_val.carbon
index 123148ead34a..6da039103aa4 100644
--- a/explorer/testdata/generic_function/return_val.carbon
+++ b/explorer/testdata/generic_function/return_val.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_function/swap.carbon b/explorer/testdata/generic_function/swap.carbon
index 8f341cbde568..be89cb1db70a 100644
--- a/explorer/testdata/generic_function/swap.carbon
+++ b/explorer/testdata/generic_function/swap.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_function/tuple_map.carbon b/explorer/testdata/generic_function/tuple_map.carbon
index 67eed0ae6c3c..06b82a789f06 100644
--- a/explorer/testdata/generic_function/tuple_map.carbon
+++ b/explorer/testdata/generic_function/tuple_map.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/generic_function/type_matching.carbon b/explorer/testdata/generic_function/type_matching.carbon
index 1955a3457eb8..7fd2db7c231b 100644
--- a/explorer/testdata/generic_function/type_matching.carbon
+++ b/explorer/testdata/generic_function/type_matching.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/global_variable/fail_init_type_mismatch.carbon b/explorer/testdata/global_variable/fail_init_type_mismatch.carbon
index 0f941d8a5c5b..c5fd8d30d0d7 100644
--- a/explorer/testdata/global_variable/fail_init_type_mismatch.carbon
+++ b/explorer/testdata/global_variable/fail_init_type_mismatch.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 // Test type checking of global variable. Error expected.
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/global_variable/fail_init_type_mismatch.carbon:[[@LINE+1]]: type error in initializer of variable: 'bool' is not implicitly convertible to 'i32'
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/global_variable/fail_init_type_mismatch.carbon:[[@LINE+1]]: type error in initializer of variable: 'bool' is not implicitly convertible to 'i32'
 var flag: i32 = true;
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/global_variable/fail_named_self.carbon b/explorer/testdata/global_variable/fail_named_self.carbon
index a22596ec5fed..f7ab098e6478 100644
--- a/explorer/testdata/global_variable/fail_named_self.carbon
+++ b/explorer/testdata/global_variable/fail_named_self.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 // Error: global variable may not be named with keyword `Self`.
-// CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/global_variable/fail_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
+// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/global_variable/fail_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
 var Self: i32 = 0;
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/global_variable/implicit_conversion.carbon b/explorer/testdata/global_variable/implicit_conversion.carbon
index 7114330d9058..d06e55ac9773 100644
--- a/explorer/testdata/global_variable/implicit_conversion.carbon
+++ b/explorer/testdata/global_variable/implicit_conversion.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 5
+// CHECK:result: 5
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/global_variable/init_and_read.carbon b/explorer/testdata/global_variable/init_and_read.carbon
index 30804c20d65c..d684d894aa46 100644
--- a/explorer/testdata/global_variable/init_and_read.carbon
+++ b/explorer/testdata/global_variable/init_and_read.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/global_variable/init_from_function.carbon b/explorer/testdata/global_variable/init_from_function.carbon
index e60f505a7b89..0b2072c17b31 100644
--- a/explorer/testdata/global_variable/init_from_function.carbon
+++ b/explorer/testdata/global_variable/init_from_function.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/global_variable/init_order.carbon b/explorer/testdata/global_variable/init_order.carbon
index 3a4fdc20df4e..9079bb4e6a6a 100644
--- a/explorer/testdata/global_variable/init_order.carbon
+++ b/explorer/testdata/global_variable/init_order.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/global_variable/shadowing.carbon b/explorer/testdata/global_variable/shadowing.carbon
index 298d46da8f20..b4fc9eb4cdb7 100644
--- a/explorer/testdata/global_variable/shadowing.carbon
+++ b/explorer/testdata/global_variable/shadowing.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/global_variable/write.carbon b/explorer/testdata/global_variable/write.carbon
index 3bc97974aeeb..db66abd5c68c 100644
--- a/explorer/testdata/global_variable/write.carbon
+++ b/explorer/testdata/global_variable/write.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/global_variable/write_from_function.carbon b/explorer/testdata/global_variable/write_from_function.carbon
index 5d3f57c0f27c..234896ef2c6a 100644
--- a/explorer/testdata/global_variable/write_from_function.carbon
+++ b/explorer/testdata/global_variable/write_from_function.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/if_else/convert_condition.carbon b/explorer/testdata/if_else/convert_condition.carbon
index 63e34fa09f0f..9ce83509ab58 100644
--- a/explorer/testdata/if_else/convert_condition.carbon
+++ b/explorer/testdata/if_else/convert_condition.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/if_else/if_else.carbon b/explorer/testdata/if_else/if_else.carbon
index de4ac083705b..d630af13f03e 100644
--- a/explorer/testdata/if_else/if_else.carbon
+++ b/explorer/testdata/if_else/if_else.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/if_else/if_else_if.carbon b/explorer/testdata/if_else/if_else_if.carbon
index deedbdb84d69..e632c0c52444 100644
--- a/explorer/testdata/if_else/if_else_if.carbon
+++ b/explorer/testdata/if_else/if_else_if.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/if_else/if_else_if_else.carbon b/explorer/testdata/if_else/if_else_if_else.carbon
index a1db8dcf72b5..0070b11bc3c6 100644
--- a/explorer/testdata/if_else/if_else_if_else.carbon
+++ b/explorer/testdata/if_else/if_else_if_else.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/if_else/if_false.carbon b/explorer/testdata/if_else/if_false.carbon
index 58c0aefaa92c..3c14a38b50d3 100644
--- a/explorer/testdata/if_else/if_false.carbon
+++ b/explorer/testdata/if_else/if_false.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/if_else/if_nesting.carbon b/explorer/testdata/if_else/if_nesting.carbon
index 7289aa595310..ce8875c22158 100644
--- a/explorer/testdata/if_else/if_nesting.carbon
+++ b/explorer/testdata/if_else/if_nesting.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/if_else/if_true.carbon b/explorer/testdata/if_else/if_true.carbon
index fe123a969a66..925a1e9ad10e 100644
--- a/explorer/testdata/if_else/if_true.carbon
+++ b/explorer/testdata/if_else/if_true.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/if_expression/convert_condition.carbon b/explorer/testdata/if_expression/convert_condition.carbon
index 3bc3fa124eaf..3beb412a2640 100644
--- a/explorer/testdata/if_expression/convert_condition.carbon
+++ b/explorer/testdata/if_expression/convert_condition.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/if_expression/if_then_else.carbon b/explorer/testdata/if_expression/if_then_else.carbon
index aa32a1aed16f..5468e5501640 100644
--- a/explorer/testdata/if_expression/if_then_else.carbon
+++ b/explorer/testdata/if_expression/if_then_else.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 12
+// CHECK:result: 12
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/impl/deducible_parameter.carbon b/explorer/testdata/impl/deducible_parameter.carbon
index 2bf1bbe6c321..f89e6e17ddf1 100644
--- a/explorer/testdata/impl/deducible_parameter.carbon
+++ b/explorer/testdata/impl/deducible_parameter.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/impl/fail_ambiguous_impl.carbon b/explorer/testdata/impl/fail_ambiguous_impl.carbon
index 3a21ceda258e..2dace25bcc5c 100644
--- a/explorer/testdata/impl/fail_ambiguous_impl.carbon
+++ b/explorer/testdata/impl/fail_ambiguous_impl.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 
@@ -37,7 +35,7 @@ external impl Point as Vector {
   fn Scale[me: Point](v: i32) -> Point {
       return {.x = me.x * v, .y = me.y * v};
   }
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_ambiguous_impl.carbon:[[@LINE+1]]: ambiguous implementations of interface Vector for class Point
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_ambiguous_impl.carbon:[[@LINE+1]]: ambiguous implementations of interface Vector for class Point
 }
 
 fn AddAndScaleGeneric[T:! Vector](a: T, b: T, s: i32) -> T {
diff --git a/explorer/testdata/impl/fail_ambiguous_impl_generic.carbon b/explorer/testdata/impl/fail_ambiguous_impl_generic.carbon
index 0854a76a6d03..938f9c8e9373 100644
--- a/explorer/testdata/impl/fail_ambiguous_impl_generic.carbon
+++ b/explorer/testdata/impl/fail_ambiguous_impl_generic.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -24,7 +22,7 @@ fn Main() -> i32 {
   let b: A(i32) = {};
   F(a);
   G(b);
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_ambiguous_impl_generic.carbon:[[@LINE+1]]: ambiguous implementations of interface B(T = i32) for class A(T = i32)
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_ambiguous_impl_generic.carbon:[[@LINE+1]]: ambiguous implementations of interface B(T = i32) for class A(T = i32)
   F(b);
   return 0;
 }
diff --git a/explorer/testdata/impl/fail_bad_member_kind.carbon b/explorer/testdata/impl/fail_bad_member_kind.carbon
index 72be158e69aa..4ad500830e44 100644
--- a/explorer/testdata/impl/fail_bad_member_kind.carbon
+++ b/explorer/testdata/impl/fail_bad_member_kind.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ interface A {
 }
 
 external impl i32 as A {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/impl/fail_bad_member_kind.carbon:[[@LINE+1]]: syntax error, unexpected CLASS, expecting ALIAS or FN or RIGHT_CURLY_BRACE
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/impl/fail_bad_member_kind.carbon:[[@LINE+1]]: syntax error, unexpected CLASS, expecting ALIAS or FN or RIGHT_CURLY_BRACE
   class T {}
 }
 
diff --git a/explorer/testdata/impl/fail_impl_as.carbon b/explorer/testdata/impl/fail_impl_as.carbon
index eb29d57fb4f1..fd1ad52ce7b4 100644
--- a/explorer/testdata/impl/fail_impl_as.carbon
+++ b/explorer/testdata/impl/fail_impl_as.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_impl_as.carbon:[[@LINE+1]]: expected constraint after `as`, found value of type i32
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_impl_as.carbon:[[@LINE+1]]: expected constraint after `as`, found value of type i32
 external impl i32 as i32 {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/impl/fail_impl_as_non_interface.carbon b/explorer/testdata/impl/fail_impl_as_non_interface.carbon
index 9c94b1bc2339..73dff2f1767b 100644
--- a/explorer/testdata/impl/fail_impl_as_non_interface.carbon
+++ b/explorer/testdata/impl/fail_impl_as_non_interface.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_impl_as_non_interface.carbon:[[@LINE+1]]: expected constraint after `as`, found value of type String
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_impl_as_non_interface.carbon:[[@LINE+1]]: expected constraint after `as`, found value of type String
 external impl i32 as String {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/impl/fail_impl_as_not_constraint.carbon b/explorer/testdata/impl/fail_impl_as_not_constraint.carbon
index 682ea6dafd5f..026d953f0e5b 100644
--- a/explorer/testdata/impl/fail_impl_as_not_constraint.carbon
+++ b/explorer/testdata/impl/fail_impl_as_not_constraint.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_impl_as_not_constraint.carbon:[[@LINE+1]]: expected constraint after `as`, found value of type i32
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_impl_as_not_constraint.carbon:[[@LINE+1]]: expected constraint after `as`, found value of type i32
 external impl i32 as i32 {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/impl/fail_impl_as_parameterized.carbon b/explorer/testdata/impl/fail_impl_as_parameterized.carbon
index 88789d002331..49d1201adc2f 100644
--- a/explorer/testdata/impl/fail_impl_as_parameterized.carbon
+++ b/explorer/testdata/impl/fail_impl_as_parameterized.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 interface Vector(Scalar:! Type) {
 }
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_impl_as_parameterized.carbon:[[@LINE+1]]: Expected a type, but got Vector
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_impl_as_parameterized.carbon:[[@LINE+1]]: Expected a type, but got Vector
 external impl i32 as Vector {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/impl/fail_nondeducible_parameter.carbon b/explorer/testdata/impl/fail_nondeducible_parameter.carbon
index c6bb5837f81f..c51094d8f039 100644
--- a/explorer/testdata/impl/fail_nondeducible_parameter.carbon
+++ b/explorer/testdata/impl/fail_nondeducible_parameter.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 interface A(T:! Type) {}
 interface B {}
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_nondeducible_parameter.carbon:[[@LINE+1]]: parameter `T:! Type` is not deducible from `impl i32 as interface B`
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_nondeducible_parameter.carbon:[[@LINE+1]]: parameter `T:! Type` is not deducible from `impl i32 as interface B`
 external impl forall [T:! Type] i32 as A(T) & B {}
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/impl/fail_param_interface_in_impl.carbon b/explorer/testdata/impl/fail_param_interface_in_impl.carbon
index 1baa85dbb07d..9cb15188008f 100644
--- a/explorer/testdata/impl/fail_param_interface_in_impl.carbon
+++ b/explorer/testdata/impl/fail_param_interface_in_impl.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -21,7 +19,7 @@ fn Main() -> i32 {
   let n: i32 = 0;
   CheckSimilar(true, false);
   CheckSimilar(true, n);
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_param_interface_in_impl.carbon:[[@LINE+1]]: could not find implementation of interface Similar(T = i32) for bool
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_param_interface_in_impl.carbon:[[@LINE+1]]: could not find implementation of interface Similar(T = i32) for bool
   CheckSimilar(n, false);
   return 0;
 }
diff --git a/explorer/testdata/impl/fail_unambiguous_impl_generic.carbon b/explorer/testdata/impl/fail_unambiguous_impl_generic.carbon
index 482048b46e62..c9ab20e996a7 100644
--- a/explorer/testdata/impl/fail_unambiguous_impl_generic.carbon
+++ b/explorer/testdata/impl/fail_unambiguous_impl_generic.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -46,7 +44,7 @@ fn Main() -> i32 {
   var a: Point(i32) = {.x = 1, .y = 1};
   var b: Point(i32) = {.x = 2, .y = 3};
   // TODO: This shouldn't be considered ambiguous.
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_unambiguous_impl_generic.carbon:[[@LINE+1]]: ambiguous implementations of interface Vector(T = i32) for class Point(T = i32)
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_unambiguous_impl_generic.carbon:[[@LINE+1]]: ambiguous implementations of interface Vector(T = i32) for class Point(T = i32)
   var p: Point(i32) = AddAndScaleGeneric(a, b, 5);
   return p.x - 15;
 }
diff --git a/explorer/testdata/impl/fail_unmet_impl_constraint.carbon b/explorer/testdata/impl/fail_unmet_impl_constraint.carbon
index 3e69d4280294..3795dc57b7a2 100644
--- a/explorer/testdata/impl/fail_unmet_impl_constraint.carbon
+++ b/explorer/testdata/impl/fail_unmet_impl_constraint.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 interface A {}
 interface B {}
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_unmet_impl_constraint.carbon:[[@LINE+1]]: could not find implementation of interface B for i32
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/impl/fail_unmet_impl_constraint.carbon:[[@LINE+1]]: could not find implementation of interface B for i32
 external impl i32 as A where i32 is B {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/impl/generic_method_impl.carbon b/explorer/testdata/impl/generic_method_impl.carbon
index 01d600509927..cabe33ab7807 100644
--- a/explorer/testdata/impl/generic_method_impl.carbon
+++ b/explorer/testdata/impl/generic_method_impl.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/impl/impl_constraint.carbon b/explorer/testdata/impl/impl_constraint.carbon
index 49b5f6cc216f..5be7b44f35f4 100644
--- a/explorer/testdata/impl/impl_constraint.carbon
+++ b/explorer/testdata/impl/impl_constraint.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1234
+// CHECK:result: 1234
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/impl/impl_in_generic_class.carbon b/explorer/testdata/impl/impl_in_generic_class.carbon
index 94e2f2959d32..a858329d37ab 100644
--- a/explorer/testdata/impl/impl_in_generic_class.carbon
+++ b/explorer/testdata/impl/impl_in_generic_class.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1133
+// CHECK:result: 1133
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/impl/param_impl.carbon b/explorer/testdata/impl/param_impl.carbon
index 4b67ef17c222..4029d8c897db 100644
--- a/explorer/testdata/impl/param_impl.carbon
+++ b/explorer/testdata/impl/param_impl.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/impl/param_impl2.carbon b/explorer/testdata/impl/param_impl2.carbon
index 26fd213da650..f986f00a20da 100644
--- a/explorer/testdata/impl/param_impl2.carbon
+++ b/explorer/testdata/impl/param_impl2.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/impl/param_impl_with_self.carbon b/explorer/testdata/impl/param_impl_with_self.carbon
index 8a5e8f5e4988..9eef8beab04a 100644
--- a/explorer/testdata/impl/param_impl_with_self.carbon
+++ b/explorer/testdata/impl/param_impl_with_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/impl/param_interface_in_impl.carbon b/explorer/testdata/impl/param_interface_in_impl.carbon
index 6a25f89a9350..87fd79405823 100644
--- a/explorer/testdata/impl/param_interface_in_impl.carbon
+++ b/explorer/testdata/impl/param_interface_in_impl.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/import/fail_nonexistent_library.carbon b/explorer/testdata/import/fail_nonexistent_library.carbon
index a8f74073eee7..865a5c18bf2c 100644
--- a/explorer/testdata/import/fail_nonexistent_library.carbon
+++ b/explorer/testdata/import/fail_nonexistent_library.carbon
@@ -4,12 +4,10 @@
 //
 // TODO: This SHOULD fail but doesn't presently.
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/import/fail_nonexistent_package.carbon b/explorer/testdata/import/fail_nonexistent_package.carbon
index 15ce18350daf..835f807a9f2f 100644
--- a/explorer/testdata/import/fail_nonexistent_package.carbon
+++ b/explorer/testdata/import/fail_nonexistent_package.carbon
@@ -4,12 +4,10 @@
 //
 // TODO: This SHOULD fail but doesn't presently.
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/import/fail_order.carbon b/explorer/testdata/import/fail_order.carbon
index 93724a0c3ad5..9ed469348812 100644
--- a/explorer/testdata/import/fail_order.carbon
+++ b/explorer/testdata/import/fail_order.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,5 +12,5 @@ fn Main() -> i32 {
   return 0;
 }
 
-// CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/import/fail_order.carbon:[[@LINE+1]]: syntax error, unexpected IMPORT, expecting END_OF_FILE
+// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/import/fail_order.carbon:[[@LINE+1]]: syntax error, unexpected IMPORT, expecting END_OF_FILE
 import ExplorerTest library "Nonexistent";
diff --git a/explorer/testdata/interface/class_function.carbon b/explorer/testdata/interface/class_function.carbon
index 9a27bc26c43d..4da06400a319 100644
--- a/explorer/testdata/interface/class_function.carbon
+++ b/explorer/testdata/interface/class_function.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/constrained_parameter.carbon b/explorer/testdata/interface/constrained_parameter.carbon
index e6b3a747e590..3e7468fa6d32 100644
--- a/explorer/testdata/interface/constrained_parameter.carbon
+++ b/explorer/testdata/interface/constrained_parameter.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/external_impl_point_vector.carbon b/explorer/testdata/interface/external_impl_point_vector.carbon
index 143ad3df2dc2..2c4ccf13732d 100644
--- a/explorer/testdata/interface/external_impl_point_vector.carbon
+++ b/explorer/testdata/interface/external_impl_point_vector.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/external_impl_use_self.carbon b/explorer/testdata/interface/external_impl_use_self.carbon
index cff62cf76d9f..e9bff8f6f5fb 100644
--- a/explorer/testdata/interface/external_impl_use_self.carbon
+++ b/explorer/testdata/interface/external_impl_use_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/fail_bad_member_kind.carbon b/explorer/testdata/interface/fail_bad_member_kind.carbon
index c101a5e96725..6b75a0db4f37 100644
--- a/explorer/testdata/interface/fail_bad_member_kind.carbon
+++ b/explorer/testdata/interface/fail_bad_member_kind.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 interface Bad {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/interface/fail_bad_member_kind.carbon:[[@LINE+1]]: syntax error, unexpected VAR, expecting FN or LET or RIGHT_CURLY_BRACE
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/interface/fail_bad_member_kind.carbon:[[@LINE+1]]: syntax error, unexpected VAR, expecting FN or LET or RIGHT_CURLY_BRACE
   var V: i32;
 }
 
diff --git a/explorer/testdata/interface/fail_external_impl_omit_self.carbon b/explorer/testdata/interface/fail_external_impl_omit_self.carbon
index b4fb2e34fa1d..23faf5cffa77 100644
--- a/explorer/testdata/interface/fail_external_impl_omit_self.carbon
+++ b/explorer/testdata/interface/fail_external_impl_omit_self.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -21,7 +19,7 @@ class Point {
 }
 
 // Error: need to specify which type implementing `Vector` for.
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_external_impl_omit_self.carbon:[[@LINE+1]]: could not resolve 'Self'
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_external_impl_omit_self.carbon:[[@LINE+1]]: could not resolve 'Self'
 external impl as Vector {
   fn Add[me: Point](b: Point) -> Point {
     return {.x = me.x + b.x, .y = me.y + b.y};
diff --git a/explorer/testdata/interface/fail_external_impl_self.carbon b/explorer/testdata/interface/fail_external_impl_self.carbon
index 84946129165c..6456b59570fd 100644
--- a/explorer/testdata/interface/fail_external_impl_self.carbon
+++ b/explorer/testdata/interface/fail_external_impl_self.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -20,7 +18,7 @@ class Point {
   var y: i32;
 }
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_external_impl_self.carbon:[[@LINE+1]]: could not resolve 'Self'
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_external_impl_self.carbon:[[@LINE+1]]: could not resolve 'Self'
 external impl Self as Vector {
   fn Add[me: Point](b: Point) -> Point {
     return {.x = me.x + b.x, .y = me.y + b.y};
diff --git a/explorer/testdata/interface/fail_impl_bad_member.carbon b/explorer/testdata/interface/fail_impl_bad_member.carbon
index 65d769f7d801..de901c067c67 100644
--- a/explorer/testdata/interface/fail_impl_bad_member.carbon
+++ b/explorer/testdata/interface/fail_impl_bad_member.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -24,9 +22,9 @@ class Point {
     }
     fn Scale[me: Point](v: i32) -> i32 {
       return 0;
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_impl_bad_member.carbon:[[@LINE+3]]: type error in member of implementation
-    // CHECK: expected: fn (i32) -> class Point
-    // CHECK: actual: fn (i32) -> i32
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_impl_bad_member.carbon:[[@LINE+3]]: type error in member of implementation
+    // CHECK:expected: fn (i32) -> class Point
+    // CHECK:actual: fn (i32) -> i32
     }
   }
 }
diff --git a/explorer/testdata/interface/fail_impl_missing_member.carbon b/explorer/testdata/interface/fail_impl_missing_member.carbon
index 4d7b419e828b..c5b733a812cb 100644
--- a/explorer/testdata/interface/fail_impl_missing_member.carbon
+++ b/explorer/testdata/interface/fail_impl_missing_member.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -22,7 +20,7 @@ class Point {
     fn Add[me: Point](b: Point) -> Point {
       return {.x = me.x + b.x, .y = me.y + b.y};
     }
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_impl_missing_member.carbon:[[@LINE+1]]: implementation missing Scale
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_impl_missing_member.carbon:[[@LINE+1]]: implementation missing Scale
   }
 }
 
diff --git a/explorer/testdata/interface/fail_impl_not_type.carbon b/explorer/testdata/interface/fail_impl_not_type.carbon
index 8f766098f71b..752d10380b4a 100644
--- a/explorer/testdata/interface/fail_impl_not_type.carbon
+++ b/explorer/testdata/interface/fail_impl_not_type.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 interface Vector {
   fn Zero() -> i32;
 }
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_impl_not_type.carbon:[[@LINE+1]]: Expected a type, but got "hello"
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_impl_not_type.carbon:[[@LINE+1]]: Expected a type, but got "hello"
 impl "hello" as Vector {
   fn Zero() -> i32 { return 0; }
 }
diff --git a/explorer/testdata/interface/fail_interface_missing_member.carbon b/explorer/testdata/interface/fail_interface_missing_member.carbon
index 14bbe7fb0a46..60da98fb2c18 100644
--- a/explorer/testdata/interface/fail_interface_missing_member.carbon
+++ b/explorer/testdata/interface/fail_interface_missing_member.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,7 +13,7 @@ interface Vector {
 }
 
 fn ScaleGeneric[T:! Vector](a: T, s: i32) -> T {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_interface_missing_member.carbon:[[@LINE+1]]: member access, Scale not in interface Vector
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_interface_missing_member.carbon:[[@LINE+1]]: member access, Scale not in interface Vector
   return a.Scale(s);
 }
 
diff --git a/explorer/testdata/interface/fail_no_impl.carbon b/explorer/testdata/interface/fail_no_impl.carbon
index db752f278856..832d071cb504 100644
--- a/explorer/testdata/interface/fail_no_impl.carbon
+++ b/explorer/testdata/interface/fail_no_impl.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -27,7 +25,7 @@ fn AddAndScaleGeneric[T:! Vector](a: T, b: T, s: i32) -> T {
 fn Main() -> i32 {
   var a: Point = {.x = 0, .y = 0};
   var b: Point = {.x = 2, .y = 3};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_no_impl.carbon:[[@LINE+1]]: could not find implementation of interface Vector for class Point
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_no_impl.carbon:[[@LINE+1]]: could not find implementation of interface Vector for class Point
   var p: Point = AddAndScaleGeneric(a, b, 3);
   return p.x - 6;
 }
diff --git a/explorer/testdata/interface/fail_use_symbolic_member.carbon b/explorer/testdata/interface/fail_use_symbolic_member.carbon
index 096016b327a8..7491b5ace047 100644
--- a/explorer/testdata/interface/fail_use_symbolic_member.carbon
+++ b/explorer/testdata/interface/fail_use_symbolic_member.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +12,7 @@ interface X {
   fn F() -> Type;
 }
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_use_symbolic_member.carbon:[[@LINE+1]]: member lookup for F in symbolic witness for T:! X
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/interface/fail_use_symbolic_member.carbon:[[@LINE+1]]: member lookup for F in symbolic witness for T:! X
 fn G[T:! X]() -> T.F() {
   return {};
 }
diff --git a/explorer/testdata/interface/generic_call_generic.carbon b/explorer/testdata/interface/generic_call_generic.carbon
index 9a016f1dbe0f..7102146bbb49 100644
--- a/explorer/testdata/interface/generic_call_generic.carbon
+++ b/explorer/testdata/interface/generic_call_generic.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/generic_with_two_params.carbon b/explorer/testdata/interface/generic_with_two_params.carbon
index ac50395ee781..447d459eb068 100644
--- a/explorer/testdata/interface/generic_with_two_params.carbon
+++ b/explorer/testdata/interface/generic_with_two_params.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/impl_self_interface_parameter.carbon b/explorer/testdata/interface/impl_self_interface_parameter.carbon
index 24285f26432f..bb3c339419d0 100644
--- a/explorer/testdata/interface/impl_self_interface_parameter.carbon
+++ b/explorer/testdata/interface/impl_self_interface_parameter.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/omit_self.carbon b/explorer/testdata/interface/omit_self.carbon
index 32db2d5ae0f4..a04cb878e5a4 100644
--- a/explorer/testdata/interface/omit_self.carbon
+++ b/explorer/testdata/interface/omit_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/param_with_dependent_type.carbon b/explorer/testdata/interface/param_with_dependent_type.carbon
index e8ffa9e65627..26e35d62f0d8 100644
--- a/explorer/testdata/interface/param_with_dependent_type.carbon
+++ b/explorer/testdata/interface/param_with_dependent_type.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 42
+// CHECK:result: 42
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/parameterized.carbon b/explorer/testdata/interface/parameterized.carbon
index c66d1cc71652..9ffcefc5b80c 100644
--- a/explorer/testdata/interface/parameterized.carbon
+++ b/explorer/testdata/interface/parameterized.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/tuple_vector_add_scale.carbon b/explorer/testdata/interface/tuple_vector_add_scale.carbon
index 35f6294685f6..c3078c4071d6 100644
--- a/explorer/testdata/interface/tuple_vector_add_scale.carbon
+++ b/explorer/testdata/interface/tuple_vector_add_scale.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/vector_point_add_scale.carbon b/explorer/testdata/interface/vector_point_add_scale.carbon
index 961b19c71360..343dfe3d7a19 100644
--- a/explorer/testdata/interface/vector_point_add_scale.carbon
+++ b/explorer/testdata/interface/vector_point_add_scale.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/interface/with_self.carbon b/explorer/testdata/interface/with_self.carbon
index 95c49ea532f8..0eb27e39f7fd 100644
--- a/explorer/testdata/interface/with_self.carbon
+++ b/explorer/testdata/interface/with_self.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/let/fail_function_args.carbon b/explorer/testdata/let/fail_function_args.carbon
index 1212434d9fe2..81e648bf5402 100644
--- a/explorer/testdata/let/fail_function_args.carbon
+++ b/explorer/testdata/let/fail_function_args.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn f((var x: i32, y: i32)) -> i32 {
   x = 0;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_function_args.carbon:[[@LINE+1]]: Cannot assign to rvalue 'y'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_function_args.carbon:[[@LINE+1]]: Cannot assign to rvalue 'y'
   y = 0;
   return x - 1;
 }
diff --git a/explorer/testdata/let/fail_global_assign.carbon b/explorer/testdata/let/fail_global_assign.carbon
index b8299ba57df2..2b12f25095b4 100644
--- a/explorer/testdata/let/fail_global_assign.carbon
+++ b/explorer/testdata/let/fail_global_assign.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 let x: i32 = 10;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_global_assign.carbon:[[@LINE+1]]: Cannot assign to rvalue 'x'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_global_assign.carbon:[[@LINE+1]]: Cannot assign to rvalue 'x'
   x = 0;
   return 0;
 }
diff --git a/explorer/testdata/let/fail_global_named_self.carbon b/explorer/testdata/let/fail_global_named_self.carbon
index 5afa959aeb33..5a0b5d5d0cc2 100644
--- a/explorer/testdata/let/fail_global_named_self.carbon
+++ b/explorer/testdata/let/fail_global_named_self.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 // Error: Can't use keyword `Self` as the name of a global.
-// CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/let/fail_global_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
+// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/let/fail_global_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
 let Self: i32 = 10;
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/let/fail_local_assign.carbon b/explorer/testdata/let/fail_local_assign.carbon
index d7c7ee1b86db..a9e157d89ed3 100644
--- a/explorer/testdata/let/fail_local_assign.carbon
+++ b/explorer/testdata/let/fail_local_assign.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   let x: auto = 10;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_local_assign.carbon:[[@LINE+1]]: Cannot assign to rvalue 'x'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_local_assign.carbon:[[@LINE+1]]: Cannot assign to rvalue 'x'
   x = 0;
   return 0;
 }
diff --git a/explorer/testdata/let/fail_local_named_self.carbon b/explorer/testdata/let/fail_local_named_self.carbon
index bfab9364314c..0d78917f7658 100644
--- a/explorer/testdata/let/fail_local_named_self.carbon
+++ b/explorer/testdata/let/fail_local_named_self.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   // Error: Can't use keyword `Self` as the name of a local.
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/let/fail_local_named_self.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/let/fail_local_named_self.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
   let Self: auto = 10;
   return 0;
 }
diff --git a/explorer/testdata/let/fail_match_choice.carbon b/explorer/testdata/let/fail_match_choice.carbon
index 089e6a272825..2625aaed32a1 100644
--- a/explorer/testdata/let/fail_match_choice.carbon
+++ b/explorer/testdata/let/fail_match_choice.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -27,7 +25,7 @@ fn Main() -> i32 {
       n = n - 1;
     }
     case Ints.Two(x: auto, y: auto) => {
-      // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_match_choice.carbon:[[@LINE+1]]: Cannot assign to rvalue 'x'
+      // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_match_choice.carbon:[[@LINE+1]]: Cannot assign to rvalue 'x'
       x = 0;
     }
   }
diff --git a/explorer/testdata/let/fail_method_args.carbon b/explorer/testdata/let/fail_method_args.carbon
index f0c36a058a57..7527261dfbef 100644
--- a/explorer/testdata/let/fail_method_args.carbon
+++ b/explorer/testdata/let/fail_method_args.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ class Point {
   }
 
   fn SetX[me: Point](x: i32) {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_method_args.carbon:[[@LINE+1]]: Cannot assign to rvalue 'x'
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_method_args.carbon:[[@LINE+1]]: Cannot assign to rvalue 'x'
     x = 10;
   }
 
diff --git a/explorer/testdata/let/fail_tuple_pattern_let_context.carbon b/explorer/testdata/let/fail_tuple_pattern_let_context.carbon
index 1914ea97cac5..acea767427cf 100644
--- a/explorer/testdata/let/fail_tuple_pattern_let_context.carbon
+++ b/explorer/testdata/let/fail_tuple_pattern_let_context.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +12,7 @@ fn Main() -> i32 {
   let (var a: auto, b: auto, c: auto, d: auto) = (1, 2, 3, 4);
   a = 0;
   // should fail
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_tuple_pattern_let_context.carbon:[[@LINE+1]]: Cannot assign to rvalue 'c'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/let/fail_tuple_pattern_let_context.carbon:[[@LINE+1]]: Cannot assign to rvalue 'c'
   c = 0;
   return 0;
 }
diff --git a/explorer/testdata/let/fail_tuple_pattern_let_context_nested.carbon b/explorer/testdata/let/fail_tuple_pattern_let_context_nested.carbon
index 367b67796153..1abe6becf4a7 100644
--- a/explorer/testdata/let/fail_tuple_pattern_let_context_nested.carbon
+++ b/explorer/testdata/let/fail_tuple_pattern_let_context_nested.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/let/fail_tuple_pattern_let_context_nested.carbon:[[@LINE+1]]: syntax error, unexpected LET
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/let/fail_tuple_pattern_let_context_nested.carbon:[[@LINE+1]]: syntax error, unexpected LET
   let (var a: auto, b: auto, c: auto, var (d: auto, let e: auto)) =
       (1, 2, 3, (4, 5));
   return 0;
diff --git a/explorer/testdata/let/fail_tuple_pattern_let_in_var.carbon b/explorer/testdata/let/fail_tuple_pattern_let_in_var.carbon
index 5425d423ca2a..ae9e3caf2c36 100644
--- a/explorer/testdata/let/fail_tuple_pattern_let_in_var.carbon
+++ b/explorer/testdata/let/fail_tuple_pattern_let_in_var.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/let/fail_tuple_pattern_let_in_var.carbon:[[@LINE+1]]: syntax error, unexpected LET
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/let/fail_tuple_pattern_let_in_var.carbon:[[@LINE+1]]: syntax error, unexpected LET
   var (var a: auto, b: auto, let c: auto, d: auto) = (1, 2, 3, 4);
   return 0;
 }
diff --git a/explorer/testdata/let/implicit_conversion.carbon b/explorer/testdata/let/implicit_conversion.carbon
index c6974d493109..8c2f4340dc1c 100644
--- a/explorer/testdata/let/implicit_conversion.carbon
+++ b/explorer/testdata/let/implicit_conversion.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/let/implicit_conversion_choice.carbon b/explorer/testdata/let/implicit_conversion_choice.carbon
index 3cc2864a8fe5..ad0823924d3b 100644
--- a/explorer/testdata/let/implicit_conversion_choice.carbon
+++ b/explorer/testdata/let/implicit_conversion_choice.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/let/nested_tuple_pattern.carbon b/explorer/testdata/let/nested_tuple_pattern.carbon
index 58c9c0259047..270c0e17d0d2 100644
--- a/explorer/testdata/let/nested_tuple_pattern.carbon
+++ b/explorer/testdata/let/nested_tuple_pattern.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/linked_list/linked_list.carbon b/explorer/testdata/linked_list/linked_list.carbon
index 1083cae9042a..d029e6b720a8 100644
--- a/explorer/testdata/linked_list/linked_list.carbon
+++ b/explorer/testdata/linked_list/linked_list.carbon
@@ -2,20 +2,18 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: 1
-// CHECK: 2
-// CHECK: 3
-// CHECK: 4
-// CHECK: 1
-// CHECK: 2
-// CHECK: 3
-// CHECK: 4
-// CHECK: result: 0
+// CHECK:1
+// CHECK:2
+// CHECK:3
+// CHECK:4
+// CHECK:1
+// CHECK:2
+// CHECK:3
+// CHECK:4
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/lit.cfg.py b/explorer/testdata/lit.cfg.py
deleted file mode 100644
index 0f1166f60ee2..000000000000
--- a/explorer/testdata/lit.cfg.py
+++ /dev/null
@@ -1,42 +0,0 @@
-__copyright__ = """
-Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-Exceptions. See /LICENSE for license information.
-SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-"""
-
-import lit.formats
-import os
-
-
-# This is a provided variable, ignore the undefined name warning.
-config = config  # noqa: F821
-
-
-def fullpath(relative_path):
-    return os.path.join(os.environ["TEST_SRCDIR"], relative_path)
-
-
-config.name = "lit"
-config.suffixes = [".carbon"]
-config.test_format = lit.formats.ShTest()
-
-config.substitutions.append(
-    ("%{prelude}", fullpath("carbon/explorer/data/prelude.carbon"))
-)
-config.substitutions.append(
-    (
-        "%{explorer}",
-        "%s --prelude=%s"
-        % (
-            fullpath("carbon/explorer/explorer"),
-            fullpath("carbon/explorer/data/prelude.carbon"),
-        ),
-    )
-)
-config.substitutions.append(("%{not}", fullpath("llvm-project/llvm/not")))
-config.substitutions.append(
-    (
-        "%{FileCheck}",
-        fullpath("llvm-project/llvm/FileCheck --dump-input-filter=all"),
-    )
-)
diff --git a/explorer/testdata/lit.cfg.py b/explorer/testdata/lit.cfg.py
new file mode 120000
index 000000000000..b4c4a91c593d
--- /dev/null
+++ b/explorer/testdata/lit.cfg.py
@@ -0,0 +1 @@
+../../bazel/testing/lit.cfg.py
\ No newline at end of file
diff --git a/explorer/testdata/match/any_int.carbon b/explorer/testdata/match/any_int.carbon
index 48558070c0a0..cad9035ad0a3 100644
--- a/explorer/testdata/match/any_int.carbon
+++ b/explorer/testdata/match/any_int.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/match/convert.carbon b/explorer/testdata/match/convert.carbon
index 631aad4cf669..8b8a4e3b28b3 100644
--- a/explorer/testdata/match/convert.carbon
+++ b/explorer/testdata/match/convert.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/match/exhaustive.carbon b/explorer/testdata/match/exhaustive.carbon
index b79650c3ed58..288ab518fd0a 100644
--- a/explorer/testdata/match/exhaustive.carbon
+++ b/explorer/testdata/match/exhaustive.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/match/exhaustive_bool.carbon b/explorer/testdata/match/exhaustive_bool.carbon
index 7d6b4ae77e32..bbe2e79bbcdd 100644
--- a/explorer/testdata/match/exhaustive_bool.carbon
+++ b/explorer/testdata/match/exhaustive_bool.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 2
+// CHECK:result: 2
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/match/exhaustive_exponential_8x.carbon b/explorer/testdata/match/exhaustive_exponential_8x.carbon
index 3db0d472a176..ff35cbb8b83b 100644
--- a/explorer/testdata/match/exhaustive_exponential_8x.carbon
+++ b/explorer/testdata/match/exhaustive_exponential_8x.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/match/exhaustive_exponential_series_t.carbon b/explorer/testdata/match/exhaustive_exponential_series_t.carbon
index 2a322eb43230..86656923b03d 100644
--- a/explorer/testdata/match/exhaustive_exponential_series_t.carbon
+++ b/explorer/testdata/match/exhaustive_exponential_series_t.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/match/fail_exhaustive_exponential_9x.carbon b/explorer/testdata/match/fail_exhaustive_exponential_9x.carbon
index 97de14d82782..c6a8cd1f727c 100644
--- a/explorer/testdata/match/fail_exhaustive_exponential_9x.carbon
+++ b/explorer/testdata/match/fail_exhaustive_exponential_9x.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -31,5 +29,5 @@ fn Main() -> i32 {
     case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B(), AB.A()) => { return 8; }
     case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B()) => { return 9; }
   }
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_exhaustive_exponential_9x.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_exhaustive_exponential_9x.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
 }
diff --git a/explorer/testdata/match/fail_exhaustive_exponential_series_t.carbon b/explorer/testdata/match/fail_exhaustive_exponential_series_t.carbon
index 1447d7f9ad66..a1b0d63f2442 100644
--- a/explorer/testdata/match/fail_exhaustive_exponential_series_t.carbon
+++ b/explorer/testdata/match/fail_exhaustive_exponential_series_t.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -40,5 +38,5 @@ fn Main() -> i32 {
     case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.A()) => { return 16; }
     case (_: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  _: AB,  AB.B()) => { return 17; }
   }
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_exhaustive_exponential_series_t.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_exhaustive_exponential_series_t.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
 }
diff --git a/explorer/testdata/match/fail_exhaustive_int.carbon b/explorer/testdata/match/fail_exhaustive_int.carbon
index c77e9a20a25d..7929e49a1935 100644
--- a/explorer/testdata/match/fail_exhaustive_int.carbon
+++ b/explorer/testdata/match/fail_exhaustive_int.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,7 +13,7 @@ fn A(n: i32) -> i32 {
     case 1 => { return 1; }
     case 2 => { return 2; }
   }
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_exhaustive_int.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_exhaustive_int.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/match/fail_not_alternative.carbon b/explorer/testdata/match/fail_not_alternative.carbon
index a647ee1abe56..efb0fa8a7e62 100644
--- a/explorer/testdata/match/fail_not_alternative.carbon
+++ b/explorer/testdata/match/fail_not_alternative.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: i32 = 0;
   match (x) {
-    // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/match/fail_not_alternative.carbon:[[@LINE+1]]: Alternative pattern must have the form of a field access.
+    // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/match/fail_not_alternative.carbon:[[@LINE+1]]: Alternative pattern must have the form of a field access.
     case i32(n: i32) => {
       return 1;
     }
diff --git a/explorer/testdata/match/fail_not_exhaustive.carbon b/explorer/testdata/match/fail_not_exhaustive.carbon
index cb882ba1a43e..1a28373c9f09 100644
--- a/explorer/testdata/match/fail_not_exhaustive.carbon
+++ b/explorer/testdata/match/fail_not_exhaustive.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -20,7 +18,7 @@ fn A(a: Opt, b: Opt) -> i32 {
     case (Opt.Some(n: i32), _: auto) => { return n; }
     case (_: auto, Opt.Some(n: i32)) => { return n; }
   }
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_not_exhaustive.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_not_exhaustive.carbon:[[@LINE+1]]: non-exhaustive match may allow control-flow to reach the end of a function that provides a `->` return type
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/match/fail_not_reachable.carbon b/explorer/testdata/match/fail_not_reachable.carbon
index 89e42a1f9fad..e9a6c100b380 100644
--- a/explorer/testdata/match/fail_not_reachable.carbon
+++ b/explorer/testdata/match/fail_not_reachable.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -19,7 +17,7 @@ fn A(a: Opt, b: Opt) -> i32 {
   match ((a, b)) {
     case (Opt.Some(n: i32), _: auto) => { return n; }
     case (_: auto, Opt.Some(n: i32)) => { return n; }
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_not_reachable.carbon:[[@LINE+1]]: unreachable case: all values matched by this case are matched by earlier cases
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_not_reachable.carbon:[[@LINE+1]]: unreachable case: all values matched by this case are matched by earlier cases
     case (Opt.Some(m: i32), Opt.Some(n: i32)) => { return m + n; }
   }
   return 0;
diff --git a/explorer/testdata/match/fail_not_reachable_default.carbon b/explorer/testdata/match/fail_not_reachable_default.carbon
index 596b00cfe06a..c173e8ee3907 100644
--- a/explorer/testdata/match/fail_not_reachable_default.carbon
+++ b/explorer/testdata/match/fail_not_reachable_default.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -20,7 +18,7 @@ fn A(a: Opt, b: Opt) -> i32 {
     case (Opt.None(), Opt.None()) => { return 0; }
     case (Opt.Some(n: i32), _: auto) => { return n; }
     case (_: auto, Opt.Some(n: i32)) => { return n; }
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_not_reachable_default.carbon:[[@LINE+1]]: unreachable case: all values matched by this case are matched by earlier cases
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_not_reachable_default.carbon:[[@LINE+1]]: unreachable case: all values matched by this case are matched by earlier cases
     default => { return -1; }
   }
   return 0;
diff --git a/explorer/testdata/match/fail_pattern_type_mismatch.carbon b/explorer/testdata/match/fail_pattern_type_mismatch.carbon
index 49b620e1e7eb..91b3c972cd62 100644
--- a/explorer/testdata/match/fail_pattern_type_mismatch.carbon
+++ b/explorer/testdata/match/fail_pattern_type_mismatch.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -23,9 +21,9 @@ fn Main() -> i32 {
   // expression when checking each pattern.
   match ((a, a)) {
     case (0, n: A) => { return 1; }
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_pattern_type_mismatch.carbon:[[@LINE+3]]: type error in `match` pattern type
-    // CHECK: expected: (i32, class A)
-    // CHECK: actual: (class A, i32)
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_pattern_type_mismatch.carbon:[[@LINE+3]]: type error in `match` pattern type
+    // CHECK:expected: (i32, class A)
+    // CHECK:actual: (class A, i32)
     case (n: A, 0) => { return 1; }
     case (1, 1) => { return 0; }
   }
diff --git a/explorer/testdata/match/fail_redundant_int.carbon b/explorer/testdata/match/fail_redundant_int.carbon
index 144ae4176bfc..255e4514749b 100644
--- a/explorer/testdata/match/fail_redundant_int.carbon
+++ b/explorer/testdata/match/fail_redundant_int.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn A(n: i32) -> i32 {
   match (n) {
     case 1 => { return 1; }
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_redundant_int.carbon:[[@LINE+1]]: unreachable case: all values matched by this case are matched by earlier cases
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/match/fail_redundant_int.carbon:[[@LINE+1]]: unreachable case: all values matched by this case are matched by earlier cases
     case 1 => { return 2; }
     case (_: i32) => { return 3; }
   }
diff --git a/explorer/testdata/match/int.carbon b/explorer/testdata/match/int.carbon
index 0b8088dbbd77..c3eff63c9b47 100644
--- a/explorer/testdata/match/int.carbon
+++ b/explorer/testdata/match/int.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/match/int_default.carbon b/explorer/testdata/match/int_default.carbon
index d928c0a84541..cd5a1336c1e4 100644
--- a/explorer/testdata/match/int_default.carbon
+++ b/explorer/testdata/match/int_default.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/match/no_match.carbon b/explorer/testdata/match/no_match.carbon
index 31d27ee1d60f..d2ef6872714a 100644
--- a/explorer/testdata/match/no_match.carbon
+++ b/explorer/testdata/match/no_match.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/match/placeholder.carbon b/explorer/testdata/match/placeholder.carbon
index be672479f4c2..fc187e5656cc 100644
--- a/explorer/testdata/match/placeholder.carbon
+++ b/explorer/testdata/match/placeholder.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/member_access/convert_lhs_class.carbon b/explorer/testdata/member_access/convert_lhs_class.carbon
index 29c74a36e464..077f4d4e2803 100644
--- a/explorer/testdata/member_access/convert_lhs_class.carbon
+++ b/explorer/testdata/member_access/convert_lhs_class.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package Foo api;
 
diff --git a/explorer/testdata/member_access/convert_lhs_interface.carbon b/explorer/testdata/member_access/convert_lhs_interface.carbon
index 811d3d5cf84f..06dfce8bef45 100644
--- a/explorer/testdata/member_access/convert_lhs_interface.carbon
+++ b/explorer/testdata/member_access/convert_lhs_interface.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package Foo api;
 
diff --git a/explorer/testdata/member_access/evaluate_type_before_dot.carbon b/explorer/testdata/member_access/evaluate_type_before_dot.carbon
index bc3795c3e385..e5acc39c2dbd 100644
--- a/explorer/testdata/member_access/evaluate_type_before_dot.carbon
+++ b/explorer/testdata/member_access/evaluate_type_before_dot.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Struct OK
-// CHECK: Choice OK
-// CHECK: Class OK
-// CHECK: Interface OK
-// CHECK: Constraint OK
-// CHECK: result: 0
+// CHECK:Struct OK
+// CHECK:Choice OK
+// CHECK:Class OK
+// CHECK:Interface OK
+// CHECK:Constraint OK
+// CHECK:result: 0
 
 package Foo api;
 
diff --git a/explorer/testdata/member_access/fail_qualified_non_member.carbon b/explorer/testdata/member_access/fail_qualified_non_member.carbon
index 6252ce58ebe3..4b611ba59a0f 100644
--- a/explorer/testdata/member_access/fail_qualified_non_member.carbon
+++ b/explorer/testdata/member_access/fail_qualified_non_member.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package Foo api;
@@ -13,7 +11,7 @@ fn F[me: i32]() {}
 fn Main() -> i32 {
   // TODO: It's unclear whether this is valid per the current rules. See
   // https://github.com/carbon-language/carbon-lang/pull/1122
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/member_access/fail_qualified_non_member.carbon:[[@LINE+1]]: expected name of instance member or interface member in compound member access, found fn () -> ()
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/member_access/fail_qualified_non_member.carbon:[[@LINE+1]]: expected name of instance member or interface member in compound member access, found fn () -> ()
   42.(F)();
   return 0;
 }
diff --git a/explorer/testdata/member_access/fail_vacuous_access.carbon b/explorer/testdata/member_access/fail_vacuous_access.carbon
index 140c1782dc88..9c60231bf968 100644
--- a/explorer/testdata/member_access/fail_vacuous_access.carbon
+++ b/explorer/testdata/member_access/fail_vacuous_access.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package Foo api;
@@ -17,6 +15,6 @@ class X {
 }
 fn Main() -> i32 {
   var a: X = {};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/member_access/fail_vacuous_access.carbon:[[@LINE+1]]: expected name of instance member or interface member in compound member access, found fn () -> i32
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/member_access/fail_vacuous_access.carbon:[[@LINE+1]]: expected name of instance member or interface member in compound member access, found fn () -> i32
   return a.(X.(A.F))();
 }
diff --git a/explorer/testdata/member_access/fail_vacuous_access_via_type_param.carbon b/explorer/testdata/member_access/fail_vacuous_access_via_type_param.carbon
index a47469912491..c49ce859e52f 100644
--- a/explorer/testdata/member_access/fail_vacuous_access_via_type_param.carbon
+++ b/explorer/testdata/member_access/fail_vacuous_access_via_type_param.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package Foo api;
@@ -16,7 +14,7 @@ class X {
   }
 }
 fn F[T:! A](a: T) -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/member_access/fail_vacuous_access_via_type_param.carbon:[[@LINE+1]]: expected name of instance member or interface member in compound member access, found fn () -> i32
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/member_access/fail_vacuous_access_via_type_param.carbon:[[@LINE+1]]: expected name of instance member or interface member in compound member access, found fn () -> i32
   return a.(T.F)();
 }
 fn Main() -> i32 {
diff --git a/explorer/testdata/member_access/nearly_vacuous_access_with_impl_lookup.carbon b/explorer/testdata/member_access/nearly_vacuous_access_with_impl_lookup.carbon
index fe6c1d6d053e..c3ba3c8b6219 100644
--- a/explorer/testdata/member_access/nearly_vacuous_access_with_impl_lookup.carbon
+++ b/explorer/testdata/member_access/nearly_vacuous_access_with_impl_lookup.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package Foo api;
 interface A { fn F() -> i32; }
diff --git a/explorer/testdata/member_access/nearly_vacuous_access_with_instance_binding.carbon b/explorer/testdata/member_access/nearly_vacuous_access_with_instance_binding.carbon
index 9cc8cffd7871..0c1dbb48f7a9 100644
--- a/explorer/testdata/member_access/nearly_vacuous_access_with_instance_binding.carbon
+++ b/explorer/testdata/member_access/nearly_vacuous_access_with_instance_binding.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package Foo api;
 interface A { fn F[me: Self]() -> i32; }
diff --git a/explorer/testdata/member_access/param_qualified_interface_member.carbon b/explorer/testdata/member_access/param_qualified_interface_member.carbon
index bfb8f63f810d..8116279dea64 100644
--- a/explorer/testdata/member_access/param_qualified_interface_member.carbon
+++ b/explorer/testdata/member_access/param_qualified_interface_member.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package Foo api;
 interface A {
diff --git a/explorer/testdata/member_access/qualified_class_member.carbon b/explorer/testdata/member_access/qualified_class_member.carbon
index c2e16ab4f13e..4cb975cd3dde 100644
--- a/explorer/testdata/member_access/qualified_class_member.carbon
+++ b/explorer/testdata/member_access/qualified_class_member.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package Foo api;
 class X {
diff --git a/explorer/testdata/member_access/qualified_constraint_member.carbon b/explorer/testdata/member_access/qualified_constraint_member.carbon
index ed62b95a7398..3a3bc295c716 100644
--- a/explorer/testdata/member_access/qualified_constraint_member.carbon
+++ b/explorer/testdata/member_access/qualified_constraint_member.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 12
+// CHECK:result: 12
 
 package Foo api;
 interface A {
diff --git a/explorer/testdata/member_access/qualified_interface_member.carbon b/explorer/testdata/member_access/qualified_interface_member.carbon
index 77fca174a6f3..8c7e2cd79b12 100644
--- a/explorer/testdata/member_access/qualified_interface_member.carbon
+++ b/explorer/testdata/member_access/qualified_interface_member.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package Foo api;
 interface A {
diff --git a/explorer/testdata/member_access/qualified_param_member.carbon b/explorer/testdata/member_access/qualified_param_member.carbon
index e3d16d6f94b7..9bd0fd2c34a2 100644
--- a/explorer/testdata/member_access/qualified_param_member.carbon
+++ b/explorer/testdata/member_access/qualified_param_member.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package Foo api;
 interface A {
diff --git a/explorer/testdata/member_access/qualified_struct_member.carbon b/explorer/testdata/member_access/qualified_struct_member.carbon
index 5a1076c176d7..e5bc2e4aa615 100644
--- a/explorer/testdata/member_access/qualified_struct_member.carbon
+++ b/explorer/testdata/member_access/qualified_struct_member.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 2
+// CHECK:result: 2
 
 package Foo api;
 fn Main() -> i32 {
diff --git a/explorer/testdata/member_access/type_qualified_interface_member.carbon b/explorer/testdata/member_access/type_qualified_interface_member.carbon
index b95a0ef3f4d0..78d5509ca69d 100644
--- a/explorer/testdata/member_access/type_qualified_interface_member.carbon
+++ b/explorer/testdata/member_access/type_qualified_interface_member.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 42
+// CHECK:result: 42
 
 package Foo api;
 interface HasDefault {
diff --git a/explorer/testdata/mixin/fail_circular_mixing.carbon b/explorer/testdata/mixin/fail_circular_mixing.carbon
index 13bf3d19506c..2e428995eafd 100644
--- a/explorer/testdata/mixin/fail_circular_mixing.carbon
+++ b/explorer/testdata/mixin/fail_circular_mixing.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 package ExplorerTest api;
 
@@ -13,7 +11,7 @@ __mixin M1 {
   fn F1[me: Self](x: Self) -> Self{
      return x;
   }
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_circular_mixing.carbon:[[@LINE+1]]: 'M3' has not been declared yet
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_circular_mixing.carbon:[[@LINE+1]]: 'M3' has not been declared yet
   __mix M3;
 }
 
diff --git a/explorer/testdata/mixin/fail_field_member_name_clash.carbon b/explorer/testdata/mixin/fail_field_member_name_clash.carbon
index f0e5f6acfbee..6123b18d9798 100644
--- a/explorer/testdata/mixin/fail_field_member_name_clash.carbon
+++ b/explorer/testdata/mixin/fail_field_member_name_clash.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -19,7 +17,7 @@ __mixin M {
 class C {
   let F: i32 = 0;
   __mix M;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_field_member_name_clash.carbon:[[@LINE+1]]: Member named F (declared at {{.*}}/explorer/testdata/mixin/fail_field_member_name_clash.carbon:16) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail_field_member_name_clash.carbon:20)
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_field_member_name_clash.carbon:[[@LINE+1]]: Member named F (declared at {{.*}}/explorer/testdata/mixin/fail_field_member_name_clash.carbon:14) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail_field_member_name_clash.carbon:18)
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/mixin/fail_method_member_name_clash.carbon b/explorer/testdata/mixin/fail_method_member_name_clash.carbon
index 2b18c62df677..c80d50cf7c35 100644
--- a/explorer/testdata/mixin/fail_method_member_name_clash.carbon
+++ b/explorer/testdata/mixin/fail_method_member_name_clash.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -21,7 +19,7 @@ class C {
      return x;
   }
   __mix M;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_method_member_name_clash.carbon:[[@LINE+1]]: Member named F (declared at {{.*}}/explorer/testdata/mixin/fail_method_member_name_clash.carbon:16) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail_method_member_name_clash.carbon:22)
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_method_member_name_clash.carbon:[[@LINE+1]]: Member named F (declared at {{.*}}/explorer/testdata/mixin/fail_method_member_name_clash.carbon:14) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail_method_member_name_clash.carbon:20)
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/mixin/fail_mix_as_type_expr.carbon b/explorer/testdata/mixin/fail_mix_as_type_expr.carbon
index b1fa73cdeed9..2871f92f8efa 100644
--- a/explorer/testdata/mixin/fail_mix_as_type_expr.carbon
+++ b/explorer/testdata/mixin/fail_mix_as_type_expr.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 __mixin Operations {}
 
 fn Main() -> i32 {
-   // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_as_type_expr.carbon:[[@LINE+1]]: Expected a type, but got mixin Operations
+   // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_as_type_expr.carbon:[[@LINE+1]]: Expected a type, but got mixin Operations
    var a: Operations;
    return 0;
 }
diff --git a/explorer/testdata/mixin/fail_mix_diamond_clash.carbon b/explorer/testdata/mixin/fail_mix_diamond_clash.carbon
index e7b7bf5318bf..a295a30b430d 100644
--- a/explorer/testdata/mixin/fail_mix_diamond_clash.carbon
+++ b/explorer/testdata/mixin/fail_mix_diamond_clash.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 package ExplorerTest api;
 
@@ -30,7 +28,7 @@ __mixin M3 {
 class C {
   __mix M2;
   __mix M3;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_diamond_clash.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail_mix_diamond_clash.carbon:15) is being mixed multiple times into C
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_diamond_clash.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail_mix_diamond_clash.carbon:13) is being mixed multiple times into C
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/mixin/fail_mix_in_global.carbon b/explorer/testdata/mixin/fail_mix_in_global.carbon
index 39f99f4e7bb5..e0912613b361 100644
--- a/explorer/testdata/mixin/fail_mix_in_global.carbon
+++ b/explorer/testdata/mixin/fail_mix_in_global.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,7 +14,7 @@ __mixin Operations {
   }
 }
 
-// CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_in_global.carbon:[[@LINE+1]]: syntax error, unexpected MIX, expecting END_OF_FILE
+// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_in_global.carbon:[[@LINE+1]]: syntax error, unexpected MIX, expecting END_OF_FILE
 __mix Operations;
 
 class Point {
diff --git a/explorer/testdata/mixin/fail_mix_in_impl.carbon b/explorer/testdata/mixin/fail_mix_in_impl.carbon
index 2fb52bf159e8..c1fa313bd457 100644
--- a/explorer/testdata/mixin/fail_mix_in_impl.carbon
+++ b/explorer/testdata/mixin/fail_mix_in_impl.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -21,7 +19,7 @@ interface A {
 }
 
 external impl i32 as A {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_in_impl.carbon:[[@LINE+1]]: syntax error, unexpected MIX, expecting ALIAS or FN or RIGHT_CURLY_BRACE
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_in_impl.carbon:[[@LINE+1]]: syntax error, unexpected MIX, expecting ALIAS or FN or RIGHT_CURLY_BRACE
   __mix Operations;
   fn F() {}
 }
diff --git a/explorer/testdata/mixin/fail_mix_members_clash.carbon b/explorer/testdata/mixin/fail_mix_members_clash.carbon
index 183e345d7e20..c9eac843fe81 100644
--- a/explorer/testdata/mixin/fail_mix_members_clash.carbon
+++ b/explorer/testdata/mixin/fail_mix_members_clash.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 package ExplorerTest api;
 
@@ -23,7 +21,7 @@ __mixin M2 {
 class C {
   __mix M1;
   __mix M2;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_members_clash.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail_mix_members_clash.carbon:20) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail_mix_members_clash.carbon:15)
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_members_clash.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail_mix_members_clash.carbon:18) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail_mix_members_clash.carbon:13)
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/mixin/fail_recursive_mixing.carbon b/explorer/testdata/mixin/fail_recursive_mixing.carbon
index 70267364ecb1..95dc11748009 100644
--- a/explorer/testdata/mixin/fail_recursive_mixing.carbon
+++ b/explorer/testdata/mixin/fail_recursive_mixing.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 package ExplorerTest api;
 
@@ -14,7 +12,7 @@ __mixin M1 {
      return x;
   }
   __mix M1;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_recursive_mixing.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail_recursive_mixing.carbon:15) is being mixed multiple times into M1
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_recursive_mixing.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail_recursive_mixing.carbon:13) is being mixed multiple times into M1
 }
 
 class C {
diff --git a/explorer/testdata/mixin/fail_self_substitution.carbon b/explorer/testdata/mixin/fail_self_substitution.carbon
index cd117b0a8434..b0834d080f41 100644
--- a/explorer/testdata/mixin/fail_self_substitution.carbon
+++ b/explorer/testdata/mixin/fail_self_substitution.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -38,7 +36,7 @@ class Complex {
 fn Main() -> i32 {
   var p: Point = Point.Origin();
   var c: Complex = {.r = 42, .i = 1};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_self_substitution.carbon:[[@LINE+1]]: type error in call: 'class Complex' is not implicitly convertible to 'class Point'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_self_substitution.carbon:[[@LINE+1]]: type error in call: 'class Complex' is not implicitly convertible to 'class Point'
   var p1: Point = p.F(c);
 
   return p1.x - 42;
diff --git a/explorer/testdata/mixin/self_substitution.carbon b/explorer/testdata/mixin/self_substitution.carbon
index d66f78f19d65..e99d89c69c5c 100644
--- a/explorer/testdata/mixin/self_substitution.carbon
+++ b/explorer/testdata/mixin/self_substitution.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/mixin/simple_mix_in_mixin.carbon b/explorer/testdata/mixin/simple_mix_in_mixin.carbon
index 0e0012e668bb..dd092736fc7c 100644
--- a/explorer/testdata/mixin/simple_mix_in_mixin.carbon
+++ b/explorer/testdata/mixin/simple_mix_in_mixin.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/mixin/simple_reuse.carbon b/explorer/testdata/mixin/simple_reuse.carbon
index 855e1310f054..8bfe216f707c 100644
--- a/explorer/testdata/mixin/simple_reuse.carbon
+++ b/explorer/testdata/mixin/simple_reuse.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/mixin/use_mixin_method_in_class_method.carbon b/explorer/testdata/mixin/use_mixin_method_in_class_method.carbon
index bd0b5687b5ee..eb70ac72f5fa 100644
--- a/explorer/testdata/mixin/use_mixin_method_in_class_method.carbon
+++ b/explorer/testdata/mixin/use_mixin_method_in_class_method.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/name_lookup/class_fn_body_reorder.carbon b/explorer/testdata/name_lookup/class_fn_body_reorder.carbon
index 2c7b60869978..3b577dfb2c81 100644
--- a/explorer/testdata/name_lookup/class_fn_body_reorder.carbon
+++ b/explorer/testdata/name_lookup/class_fn_body_reorder.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/name_lookup/fail_block_duplicate.carbon b/explorer/testdata/name_lookup/fail_block_duplicate.carbon
index cb394809df37..0c81e5ead523 100644
--- a/explorer/testdata/name_lookup/fail_block_duplicate.carbon
+++ b/explorer/testdata/name_lookup/fail_block_duplicate.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32 = 0;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_block_duplicate.carbon:[[@LINE+1]]: Duplicate name `x` also found at {{.*}}/explorer/testdata/name_lookup/fail_block_duplicate.carbon:14
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_block_duplicate.carbon:[[@LINE+1]]: Duplicate name `x` also found at {{.*}}/explorer/testdata/name_lookup/fail_block_duplicate.carbon:12
   var x: i32 = 0;
   return 0;
 }
diff --git a/explorer/testdata/name_lookup/fail_choice_duplicate.carbon b/explorer/testdata/name_lookup/fail_choice_duplicate.carbon
index 0de0d5ee4df2..903037dce0d9 100644
--- a/explorer/testdata/name_lookup/fail_choice_duplicate.carbon
+++ b/explorer/testdata/name_lookup/fail_choice_duplicate.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 choice Ints {
   None,
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_choice_duplicate.carbon:[[@LINE+1]]: Duplicate name `None` in choice type
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_choice_duplicate.carbon:[[@LINE+1]]: Duplicate name `None` in choice type
   None,
 }
 
diff --git a/explorer/testdata/name_lookup/fail_class_duplicate.carbon b/explorer/testdata/name_lookup/fail_class_duplicate.carbon
index 3178ac1de59c..7cac7f7aff17 100644
--- a/explorer/testdata/name_lookup/fail_class_duplicate.carbon
+++ b/explorer/testdata/name_lookup/fail_class_duplicate.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 class Foo {
   var x: i32;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_class_duplicate.carbon:[[@LINE+1]]: Duplicate name `x` also found at {{.*}}/explorer/testdata/name_lookup/fail_class_duplicate.carbon:14
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_class_duplicate.carbon:[[@LINE+1]]: Duplicate name `x` also found at {{.*}}/explorer/testdata/name_lookup/fail_class_duplicate.carbon:12
   var x: i32;
 }
 
diff --git a/explorer/testdata/name_lookup/fail_class_fn_use_before_declaration.carbon b/explorer/testdata/name_lookup/fail_class_fn_use_before_declaration.carbon
index 8ed8ec5886f9..afcbba988c0c 100644
--- a/explorer/testdata/name_lookup/fail_class_fn_use_before_declaration.carbon
+++ b/explorer/testdata/name_lookup/fail_class_fn_use_before_declaration.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -21,7 +19,7 @@ class A {
     return 0;
   }
 
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_class_fn_use_before_declaration.carbon:[[@LINE+1]]: 'I' has not been declared yet
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_class_fn_use_before_declaration.carbon:[[@LINE+1]]: 'I' has not been declared yet
   fn H() -> I() {
     return 0;
   }
diff --git a/explorer/testdata/name_lookup/fail_class_use_in_params.carbon b/explorer/testdata/name_lookup/fail_class_use_in_params.carbon
index 0970cb35cb46..c31f34f82c43 100644
--- a/explorer/testdata/name_lookup/fail_class_use_in_params.carbon
+++ b/explorer/testdata/name_lookup/fail_class_use_in_params.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_class_use_in_params.carbon:[[@LINE+1]]: 'A' is not usable until after it has been completely declared
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_class_use_in_params.carbon:[[@LINE+1]]: 'A' is not usable until after it has been completely declared
 class A(X:! A(i32)) {
 }
 
diff --git a/explorer/testdata/name_lookup/fail_fn_use_in_param.carbon b/explorer/testdata/name_lookup/fail_fn_use_in_param.carbon
index 8788c11c0683..0fed8e48aa8f 100644
--- a/explorer/testdata/name_lookup/fail_fn_use_in_param.carbon
+++ b/explorer/testdata/name_lookup/fail_fn_use_in_param.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_fn_use_in_param.carbon:[[@LINE+1]]: 'F' is not usable until after it has been completely declared
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_fn_use_in_param.carbon:[[@LINE+1]]: 'F' is not usable until after it has been completely declared
 fn F(x: F(0)) -> Type {
   return i32;
 }
diff --git a/explorer/testdata/name_lookup/fail_fn_use_in_return_type.carbon b/explorer/testdata/name_lookup/fail_fn_use_in_return_type.carbon
index 5013c42734a9..dbe7aaa688a2 100644
--- a/explorer/testdata/name_lookup/fail_fn_use_in_return_type.carbon
+++ b/explorer/testdata/name_lookup/fail_fn_use_in_return_type.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_fn_use_in_return_type.carbon:[[@LINE+1]]: 'F' is not usable until after it has been completely declared
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_fn_use_in_return_type.carbon:[[@LINE+1]]: 'F' is not usable until after it has been completely declared
 fn F() -> F() {
   return Type;
 }
diff --git a/explorer/testdata/name_lookup/fail_global_duplicate.carbon b/explorer/testdata/name_lookup/fail_global_duplicate.carbon
index 319a13416134..c110a0f55f55 100644
--- a/explorer/testdata/name_lookup/fail_global_duplicate.carbon
+++ b/explorer/testdata/name_lookup/fail_global_duplicate.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 var x: i32 = 0;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_global_duplicate.carbon:[[@LINE+1]]: Duplicate name `x` also found at {{.*}}/explorer/testdata/name_lookup/fail_global_duplicate.carbon:13
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_global_duplicate.carbon:[[@LINE+1]]: Duplicate name `x` also found at {{.*}}/explorer/testdata/name_lookup/fail_global_duplicate.carbon:11
 var x: i32 = 0;
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/name_lookup/fail_use_before_declare.carbon b/explorer/testdata/name_lookup/fail_use_before_declare.carbon
index e693f772db5f..d720ff0e9397 100644
--- a/explorer/testdata/name_lookup/fail_use_before_declare.carbon
+++ b/explorer/testdata/name_lookup/fail_use_before_declare.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_use_before_declare.carbon:[[@LINE+1]]: could not resolve 'x'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_use_before_declare.carbon:[[@LINE+1]]: could not resolve 'x'
   x = 0;
   var x: i32 = 0;
   return 0;
diff --git a/explorer/testdata/name_lookup/fail_var_use_before_declaration.carbon b/explorer/testdata/name_lookup/fail_var_use_before_declaration.carbon
index 1f44b45317ce..445ed8c9a7d9 100644
--- a/explorer/testdata/name_lookup/fail_var_use_before_declaration.carbon
+++ b/explorer/testdata/name_lookup/fail_var_use_before_declaration.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 // Test that a global variable may not depend on a later global.
 // Error expected.
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_var_use_before_declaration.carbon:[[@LINE+1]]: 'y' has not been declared yet
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/name_lookup/fail_var_use_before_declaration.carbon:[[@LINE+1]]: 'y' has not been declared yet
 var x: i32 = y;
 
 var y: i32 = 0;
diff --git a/explorer/testdata/name_lookup/global_shadow.carbon b/explorer/testdata/name_lookup/global_shadow.carbon
index aebe34d86ff6..d53f81dffd6f 100644
--- a/explorer/testdata/name_lookup/global_shadow.carbon
+++ b/explorer/testdata/name_lookup/global_shadow.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/name_lookup/match_shadow.carbon b/explorer/testdata/name_lookup/match_shadow.carbon
index 572ec03d2d42..88cbd94e4ac0 100644
--- a/explorer/testdata/name_lookup/match_shadow.carbon
+++ b/explorer/testdata/name_lookup/match_shadow.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/add.carbon b/explorer/testdata/operators/add.carbon
index 6bf042244704..a54e57e95011 100644
--- a/explorer/testdata/operators/add.carbon
+++ b/explorer/testdata/operators/add.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 6
+// CHECK:result: 6
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/add_builtin.carbon b/explorer/testdata/operators/add_builtin.carbon
index e61291de95ea..d1fb03952aec 100644
--- a/explorer/testdata/operators/add_builtin.carbon
+++ b/explorer/testdata/operators/add_builtin.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Interface: 5
-// CHECK: Op: 5
-// CHECK: result: 0
+// CHECK:Interface: 5
+// CHECK:Op: 5
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/bit_and.carbon b/explorer/testdata/operators/bit_and.carbon
index 08f633ad8576..92b7bac58eeb 100644
--- a/explorer/testdata/operators/bit_and.carbon
+++ b/explorer/testdata/operators/bit_and.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/bit_complement.carbon b/explorer/testdata/operators/bit_complement.carbon
index ee13e9ac3ca1..e9b2f5ec077b 100644
--- a/explorer/testdata/operators/bit_complement.carbon
+++ b/explorer/testdata/operators/bit_complement.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: -6
+// CHECK:result: -6
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/bit_or.carbon b/explorer/testdata/operators/bit_or.carbon
index 3487110474bc..d6e4117e69de 100644
--- a/explorer/testdata/operators/bit_or.carbon
+++ b/explorer/testdata/operators/bit_or.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 5
+// CHECK:result: 5
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/bit_xor.carbon b/explorer/testdata/operators/bit_xor.carbon
index d9255cb39e18..d3f7f61d4421 100644
--- a/explorer/testdata/operators/bit_xor.carbon
+++ b/explorer/testdata/operators/bit_xor.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 4
+// CHECK:result: 4
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/bitwise.carbon b/explorer/testdata/operators/bitwise.carbon
index ec82042d997c..93de60c8a113 100644
--- a/explorer/testdata/operators/bitwise.carbon
+++ b/explorer/testdata/operators/bitwise.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/div.carbon b/explorer/testdata/operators/div.carbon
index c15176a94330..0fc7076987e2 100644
--- a/explorer/testdata/operators/div.carbon
+++ b/explorer/testdata/operators/div.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 2
+// CHECK:result: 2
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/div_builtin.carbon b/explorer/testdata/operators/div_builtin.carbon
index e73a4e3fc8e2..4af51e5711dc 100644
--- a/explorer/testdata/operators/div_builtin.carbon
+++ b/explorer/testdata/operators/div_builtin.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Interface: 2
-// CHECK: Op: 2
-// CHECK: result: 0
+// CHECK:Interface: 2
+// CHECK:Op: 2
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/fail_no_add.carbon b/explorer/testdata/operators/fail_no_add.carbon
index 4d063eadd422..2d225fd319d4 100644
--- a/explorer/testdata/operators/fail_no_add.carbon
+++ b/explorer/testdata/operators/fail_no_add.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,8 +12,8 @@ class A {}
 
 fn Main() -> i32 {
   var a: A = {};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/operators/fail_no_add.carbon:[[@LINE+2]]: type error in `+`:
-  // CHECK: could not find implementation of interface AddWith(U = i32) for class A
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/operators/fail_no_add.carbon:[[@LINE+2]]: type error in `+`:
+  // CHECK:could not find implementation of interface AddWith(U = i32) for class A
   a + 1;
   return 0;
 }
diff --git a/explorer/testdata/operators/fail_no_mul.carbon b/explorer/testdata/operators/fail_no_mul.carbon
index 0b6ab1fcc712..53b26126de5d 100644
--- a/explorer/testdata/operators/fail_no_mul.carbon
+++ b/explorer/testdata/operators/fail_no_mul.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,8 +12,8 @@ class A {}
 
 fn Main() -> i32 {
   var a: A = {};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/operators/fail_no_mul.carbon:[[@LINE+2]]: type error in `*`:
-  // CHECK: could not find implementation of interface MulWith(U = i32) for class A
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/operators/fail_no_mul.carbon:[[@LINE+2]]: type error in `*`:
+  // CHECK:could not find implementation of interface MulWith(U = i32) for class A
   a * 1;
   return 0;
 }
diff --git a/explorer/testdata/operators/fail_no_negate.carbon b/explorer/testdata/operators/fail_no_negate.carbon
index 249ffcdbf455..b5f11b13cfa1 100644
--- a/explorer/testdata/operators/fail_no_negate.carbon
+++ b/explorer/testdata/operators/fail_no_negate.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,8 +12,8 @@ class A {}
 
 fn Main() -> i32 {
   var a: A = {};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/operators/fail_no_negate.carbon:[[@LINE+2]]: type error in `-`:
-  // CHECK: could not find implementation of interface Negate for class A
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/operators/fail_no_negate.carbon:[[@LINE+2]]: type error in `-`:
+  // CHECK:could not find implementation of interface Negate for class A
   -a;
   return 0;
 }
diff --git a/explorer/testdata/operators/fail_no_sub.carbon b/explorer/testdata/operators/fail_no_sub.carbon
index 492d54c35342..791228f60740 100644
--- a/explorer/testdata/operators/fail_no_sub.carbon
+++ b/explorer/testdata/operators/fail_no_sub.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,8 +12,8 @@ class A {}
 
 fn Main() -> i32 {
   var a: A = {};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/operators/fail_no_sub.carbon:[[@LINE+2]]: type error in `-`:
-  // CHECK: could not find implementation of interface SubWith(U = i32) for class A
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/operators/fail_no_sub.carbon:[[@LINE+2]]: type error in `-`:
+  // CHECK:could not find implementation of interface SubWith(U = i32) for class A
   a - 1;
   return 0;
 }
diff --git a/explorer/testdata/operators/left_shift.carbon b/explorer/testdata/operators/left_shift.carbon
index 02ec75e691ea..536ef8f7d45a 100644
--- a/explorer/testdata/operators/left_shift.carbon
+++ b/explorer/testdata/operators/left_shift.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 10
+// CHECK:result: 10
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/mod.carbon b/explorer/testdata/operators/mod.carbon
index 336671c00bcd..5d6cd6a5fb60 100644
--- a/explorer/testdata/operators/mod.carbon
+++ b/explorer/testdata/operators/mod.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/mod_builtin.carbon b/explorer/testdata/operators/mod_builtin.carbon
index cf3f2f753ed2..176bfa58b49c 100644
--- a/explorer/testdata/operators/mod_builtin.carbon
+++ b/explorer/testdata/operators/mod_builtin.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Interface: 2
-// CHECK: Op: 2
-// CHECK: result: 0
+// CHECK:Interface: 2
+// CHECK:Op: 2
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/mod_edges.carbon b/explorer/testdata/operators/mod_edges.carbon
index 8350cea2c89f..2f81cf592f76 100644
--- a/explorer/testdata/operators/mod_edges.carbon
+++ b/explorer/testdata/operators/mod_edges.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/mul.carbon b/explorer/testdata/operators/mul.carbon
index a9c89c4f93f8..a0ebb723cee3 100644
--- a/explorer/testdata/operators/mul.carbon
+++ b/explorer/testdata/operators/mul.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 10
+// CHECK:result: 10
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/mul_builtin.carbon b/explorer/testdata/operators/mul_builtin.carbon
index 563fdcc63b5b..74de6e22bee6 100644
--- a/explorer/testdata/operators/mul_builtin.carbon
+++ b/explorer/testdata/operators/mul_builtin.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Interface: 6
-// CHECK: Op: 6
-// CHECK: result: 0
+// CHECK:Interface: 6
+// CHECK:Op: 6
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/negate.carbon b/explorer/testdata/operators/negate.carbon
index 2b2a32c93421..b48ffa6970fc 100644
--- a/explorer/testdata/operators/negate.carbon
+++ b/explorer/testdata/operators/negate.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: -5
+// CHECK:result: -5
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/negate_builtin.carbon b/explorer/testdata/operators/negate_builtin.carbon
index a9999d717118..de13666db2fc 100644
--- a/explorer/testdata/operators/negate_builtin.carbon
+++ b/explorer/testdata/operators/negate_builtin.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Interface: -3
-// CHECK: Op: -3
-// CHECK: result: 0
+// CHECK:Interface: -3
+// CHECK:Op: -3
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/right_shift.carbon b/explorer/testdata/operators/right_shift.carbon
index c539dedac4d6..1a3aae50d4e7 100644
--- a/explorer/testdata/operators/right_shift.carbon
+++ b/explorer/testdata/operators/right_shift.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 2
+// CHECK:result: 2
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/shift.carbon b/explorer/testdata/operators/shift.carbon
index 920e706887ab..fbe571c3db32 100644
--- a/explorer/testdata/operators/shift.carbon
+++ b/explorer/testdata/operators/shift.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/shortcircuit_and.carbon b/explorer/testdata/operators/shortcircuit_and.carbon
index 0f789bbdc719..91f64db75e88 100644
--- a/explorer/testdata/operators/shortcircuit_and.carbon
+++ b/explorer/testdata/operators/shortcircuit_and.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/shortcircuit_and_no_shortcircuit.carbon b/explorer/testdata/operators/shortcircuit_and_no_shortcircuit.carbon
index 2d97faa60db9..ad568e46d6f3 100644
--- a/explorer/testdata/operators/shortcircuit_and_no_shortcircuit.carbon
+++ b/explorer/testdata/operators/shortcircuit_and_no_shortcircuit.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 2
+// CHECK:result: 2
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/shortcircuit_or.carbon b/explorer/testdata/operators/shortcircuit_or.carbon
index 1f1e4427e4a2..4572f98195a7 100644
--- a/explorer/testdata/operators/shortcircuit_or.carbon
+++ b/explorer/testdata/operators/shortcircuit_or.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/shortcircuit_or_no_shortcircuit.carbon b/explorer/testdata/operators/shortcircuit_or_no_shortcircuit.carbon
index d9de7b61770a..3048b03dc4fe 100644
--- a/explorer/testdata/operators/shortcircuit_or_no_shortcircuit.carbon
+++ b/explorer/testdata/operators/shortcircuit_or_no_shortcircuit.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 2
+// CHECK:result: 2
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/sub.carbon b/explorer/testdata/operators/sub.carbon
index f9ed3a4438e4..3f3564950018 100644
--- a/explorer/testdata/operators/sub.carbon
+++ b/explorer/testdata/operators/sub.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 4
+// CHECK:result: 4
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/sub_builtin.carbon b/explorer/testdata/operators/sub_builtin.carbon
index b328ad394cfc..e7ec8990cb0f 100644
--- a/explorer/testdata/operators/sub_builtin.carbon
+++ b/explorer/testdata/operators/sub_builtin.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Interface: 5
-// CHECK: Op: 5
-// CHECK: result: 0
+// CHECK:Interface: 5
+// CHECK:Op: 5
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/optional/init_optional_with_non_value.carbon b/explorer/testdata/optional/init_optional_with_non_value.carbon
index 469718cb8a92..ff8f330b1219 100644
--- a/explorer/testdata/optional/init_optional_with_non_value.carbon
+++ b/explorer/testdata/optional/init_optional_with_non_value.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/optional/init_optional_with_value.carbon b/explorer/testdata/optional/init_optional_with_value.carbon
index a55d5ecab75a..35725424ae5d 100644
--- a/explorer/testdata/optional/init_optional_with_value.carbon
+++ b/explorer/testdata/optional/init_optional_with_value.carbon
@@ -2,13 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Hallo Welt
-// CHECK: result: 0
+// CHECK:Hallo Welt
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/package/fail_missing.carbon b/explorer/testdata/package/fail_missing.carbon
index a12921624381..5f0e0ff6bd96 100644
--- a/explorer/testdata/package/fail_missing.carbon
+++ b/explorer/testdata/package/fail_missing.carbon
@@ -2,13 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
-// CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/package/fail_missing.carbon:[[@LINE+1]]: syntax error, unexpected FN, expecting PACKAGE
+// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/package/fail_missing.carbon:[[@LINE+1]]: syntax error, unexpected FN, expecting PACKAGE
 fn Main() -> i32 {
   return 0;
 }
diff --git a/explorer/testdata/package/with_library.carbon b/explorer/testdata/package/with_library.carbon
index f24aebab425e..087ee7ea39ff 100644
--- a/explorer/testdata/package/with_library.carbon
+++ b/explorer/testdata/package/with_library.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest library "Foo" api;
 
diff --git a/explorer/testdata/pointer/aliasing.carbon b/explorer/testdata/pointer/aliasing.carbon
index 9a86d02b0d1d..62139d8697d7 100644
--- a/explorer/testdata/pointer/aliasing.carbon
+++ b/explorer/testdata/pointer/aliasing.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/pointer/basic.carbon b/explorer/testdata/pointer/basic.carbon
index b970849f83f8..234d510ced62 100644
--- a/explorer/testdata/pointer/basic.carbon
+++ b/explorer/testdata/pointer/basic.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/pointer/fail_rvalue_addressof.carbon b/explorer/testdata/pointer/fail_rvalue_addressof.carbon
index f7ad7fff062c..d6adf7eb8d37 100644
--- a/explorer/testdata/pointer/fail_rvalue_addressof.carbon
+++ b/explorer/testdata/pointer/fail_rvalue_addressof.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32 = 5;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/pointer/fail_rvalue_addressof.carbon:[[@LINE+1]]: Argument to & should be an lvalue.
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/pointer/fail_rvalue_addressof.carbon:[[@LINE+1]]: Argument to & should be an lvalue.
   var p: i32* = &5;
   return 0;
 }
diff --git a/explorer/testdata/pointer/fail_use_after_free.carbon b/explorer/testdata/pointer/fail_use_after_free.carbon
index 1ecffecd840d..1ab45be58ed5 100644
--- a/explorer/testdata/pointer/fail_use_after_free.carbon
+++ b/explorer/testdata/pointer/fail_use_after_free.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,6 +11,6 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var p: i32* = heap.New(5);
   heap.Delete(p);
-  // CHECK: RUNTIME ERROR: {{.*}}/explorer/testdata/pointer/fail_use_after_free.carbon:[[@LINE+1]]: undefined behavior: access to dead value 5
+  // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/pointer/fail_use_after_free.carbon:[[@LINE+1]]: undefined behavior: access to dead value 5
   return *p;
 }
diff --git a/explorer/testdata/pointer/heap_alloc_lifetime.carbon b/explorer/testdata/pointer/heap_alloc_lifetime.carbon
index 07713afcf98a..c724d96f4e77 100644
--- a/explorer/testdata/pointer/heap_alloc_lifetime.carbon
+++ b/explorer/testdata/pointer/heap_alloc_lifetime.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/pointer/intrinsic_new.carbon b/explorer/testdata/pointer/intrinsic_new.carbon
index 7e160c26fe68..1887a7d6fe56 100644
--- a/explorer/testdata/pointer/intrinsic_new.carbon
+++ b/explorer/testdata/pointer/intrinsic_new.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/pointer/new_and_delete.carbon b/explorer/testdata/pointer/new_and_delete.carbon
index 29f578076660..14af052d813c 100644
--- a/explorer/testdata/pointer/new_and_delete.carbon
+++ b/explorer/testdata/pointer/new_and_delete.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/pointer/struct_pointer.carbon b/explorer/testdata/pointer/struct_pointer.carbon
index 743b3990b7f2..38dd6a04b0ff 100644
--- a/explorer/testdata/pointer/struct_pointer.carbon
+++ b/explorer/testdata/pointer/struct_pointer.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/print/associated_constant.carbon b/explorer/testdata/print/associated_constant.carbon
index 7d2836f61716..e125227a6314 100644
--- a/explorer/testdata/print/associated_constant.carbon
+++ b/explorer/testdata/print/associated_constant.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: i32
-// CHECK: String
-// CHECK: result: 0
+// CHECK:i32
+// CHECK:String
+// CHECK:result: 0
 
 package Testcase api;
 
diff --git a/explorer/testdata/print/fail_no_args.carbon b/explorer/testdata/print/fail_no_args.carbon
index 5a00041da720..a6619e10fb53 100644
--- a/explorer/testdata/print/fail_no_args.carbon
+++ b/explorer/testdata/print/fail_no_args.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/print/fail_no_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 0
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/print/fail_no_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 0
   Print();
   return 0;
 }
diff --git a/explorer/testdata/print/fail_not_str.carbon b/explorer/testdata/print/fail_not_str.carbon
index 3a0a13b508bd..933667109f6e 100644
--- a/explorer/testdata/print/fail_not_str.carbon
+++ b/explorer/testdata/print/fail_not_str.carbon
@@ -2,18 +2,16 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/print/fail_not_str.carbon:[[@LINE+3]]: type error in Print argument 0
-  // CHECK: expected: String
-  // CHECK: actual: {.x: i32}
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/print/fail_not_str.carbon:[[@LINE+3]]: type error in Print argument 0
+  // CHECK:expected: String
+  // CHECK:actual: {.x: i32}
   Print({.x = 1});
   return 0;
 }
diff --git a/explorer/testdata/print/fail_too_many_args.carbon b/explorer/testdata/print/fail_too_many_args.carbon
index 7d491b49787d..3b44282c33ce 100644
--- a/explorer/testdata/print/fail_too_many_args.carbon
+++ b/explorer/testdata/print/fail_too_many_args.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/print/fail_too_many_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 5
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/print/fail_too_many_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 5
   Print("too", "many", "args", "to", "print");
   return 0;
 }
diff --git a/explorer/testdata/print/fail_type.carbon b/explorer/testdata/print/fail_type.carbon
index 4ebabf38501d..d81d27b6b412 100644
--- a/explorer/testdata/print/fail_type.carbon
+++ b/explorer/testdata/print/fail_type.carbon
@@ -2,18 +2,16 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/print/fail_type.carbon:[[@LINE+3]]: type error in Print argument 1
-  // CHECK: expected: i32
-  // CHECK: actual: {.x: i32}
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/print/fail_type.carbon:[[@LINE+3]]: type error in Print argument 1
+  // CHECK:expected: i32
+  // CHECK:actual: {.x: i32}
   Print("{0}", {.x = 1});
   return 0;
 }
diff --git a/explorer/testdata/print/format_only.carbon b/explorer/testdata/print/format_only.carbon
index e7a9cc347083..f8f4b52d6209 100644
--- a/explorer/testdata/print/format_only.carbon
+++ b/explorer/testdata/print/format_only.carbon
@@ -2,13 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Hello world!
-// CHECK: result: 0
+// CHECK:Hello world!
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/print/i32.carbon b/explorer/testdata/print/i32.carbon
index d309cc9022eb..12cbcf9306a6 100644
--- a/explorer/testdata/print/i32.carbon
+++ b/explorer/testdata/print/i32.carbon
@@ -2,13 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Printing 1
-// CHECK: result: 0
+// CHECK:Printing 1
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/random/random.carbon b/explorer/testdata/random/random.carbon
index ee99e7c88651..00b612ec6fcc 100644
--- a/explorer/testdata/random/random.carbon
+++ b/explorer/testdata/random/random.carbon
@@ -2,13 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: Nice!
-// CHECK: result: 0
+// CHECK:Nice!
+// CHECK:result: 0
 
 package ExplorerTest api;
 fn test(para: i32)->bool{
diff --git a/explorer/testdata/return/convert_return_value.carbon b/explorer/testdata/return/convert_return_value.carbon
index d18fc47720bc..639e1661a7d4 100644
--- a/explorer/testdata/return/convert_return_value.carbon
+++ b/explorer/testdata/return/convert_return_value.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 42
+// CHECK:result: 42
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/return/explicit_empty.carbon b/explorer/testdata/return/explicit_empty.carbon
index 075c9bf490f6..87ad498bc9b5 100644
--- a/explorer/testdata/return/explicit_empty.carbon
+++ b/explorer/testdata/return/explicit_empty.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/return/fail_explicit_with_no_return.carbon b/explorer/testdata/return/fail_explicit_with_no_return.carbon
index 4ab9407e50c9..c768289f03d7 100644
--- a/explorer/testdata/return/fail_explicit_with_no_return.carbon
+++ b/explorer/testdata/return/fail_explicit_with_no_return.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn F() -> () {
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/return/fail_explicit_with_no_return.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
+// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/return/fail_explicit_with_no_return.carbon:[[@LINE+1]]: control-flow reaches end of function that provides a `->` return type without reaching a return statement
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/return/fail_explicit_with_plain_return.carbon b/explorer/testdata/return/fail_explicit_with_plain_return.carbon
index d6beb5242d58..569130c437ce 100644
--- a/explorer/testdata/return/fail_explicit_with_plain_return.carbon
+++ b/explorer/testdata/return/fail_explicit_with_plain_return.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn F() -> () {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/return/fail_explicit_with_plain_return.carbon:[[@LINE+1]]: return; should provide a return value, to match the function's signature.
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/return/fail_explicit_with_plain_return.carbon:[[@LINE+1]]: return; should provide a return value, to match the function's signature.
   return;
 }
 
diff --git a/explorer/testdata/return/fail_implicit_with_explicit_return.carbon b/explorer/testdata/return/fail_implicit_with_explicit_return.carbon
index ef4fc3b3c35e..43078f13232b 100644
--- a/explorer/testdata/return/fail_implicit_with_explicit_return.carbon
+++ b/explorer/testdata/return/fail_implicit_with_explicit_return.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn F() {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/return/fail_implicit_with_explicit_return.carbon:[[@LINE+1]]: return (); should not provide a return value, to match the function's signature.
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/return/fail_implicit_with_explicit_return.carbon:[[@LINE+1]]: return (); should not provide a return value, to match the function's signature.
   return ();
 }
 
diff --git a/explorer/testdata/return/implicit_with_no_return.carbon b/explorer/testdata/return/implicit_with_no_return.carbon
index d0445fbfb2c0..f9469bc270bb 100644
--- a/explorer/testdata/return/implicit_with_no_return.carbon
+++ b/explorer/testdata/return/implicit_with_no_return.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/return/implicit_with_plain_return.carbon b/explorer/testdata/return/implicit_with_plain_return.carbon
index ef4330c9b764..397c0f39814d 100644
--- a/explorer/testdata/return/implicit_with_plain_return.carbon
+++ b/explorer/testdata/return/implicit_with_plain_return.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/returned_var/fail_duplicate_return_var.carbon b/explorer/testdata/returned_var/fail_duplicate_return_var.carbon
index 2ed9ef9b661e..7aa9da9c5932 100644
--- a/explorer/testdata/returned_var/fail_duplicate_return_var.carbon
+++ b/explorer/testdata/returned_var/fail_duplicate_return_var.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn AddInt(a: i32, b: i32) -> i32 {
   returned var ret: i32 = a + b;
   if (a == b) {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_duplicate_return_var.carbon:[[@LINE+1]]: Duplicate definition of returned var also found at {{.*}}/explorer/testdata/returned_var/fail_duplicate_return_var.carbon:14
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_duplicate_return_var.carbon:[[@LINE+1]]: Duplicate definition of returned var also found at {{.*}}/explorer/testdata/returned_var/fail_duplicate_return_var.carbon:12
     returned var ret2: i32 = a + b;
   }
   return var;
diff --git a/explorer/testdata/returned_var/fail_missing_declaration.carbon b/explorer/testdata/returned_var/fail_missing_declaration.carbon
index 3b453b53a3c2..1b64d3b81c73 100644
--- a/explorer/testdata/returned_var/fail_missing_declaration.carbon
+++ b/explorer/testdata/returned_var/fail_missing_declaration.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn AddInt(a: i32, b: i32) -> i32 {
   var ret: i32 = a + b;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_missing_declaration.carbon:[[@LINE+1]]: `return var` is not allowed without a returned var defined in scope.
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_missing_declaration.carbon:[[@LINE+1]]: `return var` is not allowed without a returned var defined in scope.
   return var;
 }
 
diff --git a/explorer/testdata/returned_var/fail_missing_return.carbon b/explorer/testdata/returned_var/fail_missing_return.carbon
index 3546566c0403..e2b3c1c2b5f5 100644
--- a/explorer/testdata/returned_var/fail_missing_return.carbon
+++ b/explorer/testdata/returned_var/fail_missing_return.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn AddInt(a: i32, b: i32) -> i32 {
   returned var ret: i32 = a + b;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_missing_return.carbon:[[@LINE+1]]: `return <expression>` is not allowed with a returned var defined in scope: {{.*}}/explorer/testdata/returned_var/fail_missing_return.carbon:14
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_missing_return.carbon:[[@LINE+1]]: `return <expression>` is not allowed with a returned var defined in scope: {{.*}}/explorer/testdata/returned_var/fail_missing_return.carbon:12
   return ret;
 }
 
diff --git a/explorer/testdata/returned_var/fail_returned_var_mismatch_signature.carbon b/explorer/testdata/returned_var/fail_returned_var_mismatch_signature.carbon
index 2761a053a151..ebe72f801ac0 100644
--- a/explorer/testdata/returned_var/fail_returned_var_mismatch_signature.carbon
+++ b/explorer/testdata/returned_var/fail_returned_var_mismatch_signature.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Foo() {
   returned var x: () = ();
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_returned_var_mismatch_signature.carbon:[[@LINE+1]]: return var; should not provide a return value, to match the function's signature.
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_returned_var_mismatch_signature.carbon:[[@LINE+1]]: return var; should not provide a return value, to match the function's signature.
   return var;
 }
 
diff --git a/explorer/testdata/returned_var/fail_returned_var_multi_auto.carbon b/explorer/testdata/returned_var/fail_returned_var_multi_auto.carbon
index 3c132c29da88..7cc4ec015d46 100644
--- a/explorer/testdata/returned_var/fail_returned_var_multi_auto.carbon
+++ b/explorer/testdata/returned_var/fail_returned_var_multi_auto.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -17,7 +15,7 @@ fn Foo(a: i32, b: i32) -> auto {
     return var;
   }
   ret = a - b;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_returned_var_multi_auto.carbon:[[@LINE+1]]: Only one return is allowed in a function with an `auto` return type.
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_returned_var_multi_auto.carbon:[[@LINE+1]]: Only one return is allowed in a function with an `auto` return type.
   return var;
 }
 
diff --git a/explorer/testdata/returned_var/fail_returned_var_type_mismatch.carbon b/explorer/testdata/returned_var/fail_returned_var_type_mismatch.carbon
index 8c95bd40d330..05f45632666d 100644
--- a/explorer/testdata/returned_var/fail_returned_var_type_mismatch.carbon
+++ b/explorer/testdata/returned_var/fail_returned_var_type_mismatch.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn AddInt(a: i32, b: i32) -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_returned_var_type_mismatch.carbon:[[@LINE+1]]: type of returned var `bool` does not match return type `i32`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/returned_var/fail_returned_var_type_mismatch.carbon:[[@LINE+1]]: type of returned var `bool` does not match return type `i32`
   returned var ret: bool = true;
   return var;
 }
diff --git a/explorer/testdata/returned_var/multiple_returned_var_control_flow.carbon b/explorer/testdata/returned_var/multiple_returned_var_control_flow.carbon
index fa04b9ad2986..d0ee4c0becce 100644
--- a/explorer/testdata/returned_var/multiple_returned_var_control_flow.carbon
+++ b/explorer/testdata/returned_var/multiple_returned_var_control_flow.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/returned_var/normal_return_control_flow.carbon b/explorer/testdata/returned_var/normal_return_control_flow.carbon
index bc6c26aad3d9..dcb85df3be6c 100644
--- a/explorer/testdata/returned_var/normal_return_control_flow.carbon
+++ b/explorer/testdata/returned_var/normal_return_control_flow.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/returned_var/returned_var_auto.carbon b/explorer/testdata/returned_var/returned_var_auto.carbon
index 8234d2ba81ae..26e30ca6ac99 100644
--- a/explorer/testdata/returned_var/returned_var_auto.carbon
+++ b/explorer/testdata/returned_var/returned_var_auto.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/returned_var/returned_var_basic.carbon b/explorer/testdata/returned_var/returned_var_basic.carbon
index 83843f87ac0d..f5277918f4b5 100644
--- a/explorer/testdata/returned_var/returned_var_basic.carbon
+++ b/explorer/testdata/returned_var/returned_var_basic.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/returned_var/returned_var_name_lookup.carbon b/explorer/testdata/returned_var/returned_var_name_lookup.carbon
index 5543562711e3..b512fd71c5a3 100644
--- a/explorer/testdata/returned_var/returned_var_name_lookup.carbon
+++ b/explorer/testdata/returned_var/returned_var_name_lookup.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/returned_var/returned_var_omitted_expression.carbon b/explorer/testdata/returned_var/returned_var_omitted_expression.carbon
index bc21a1e5ad25..2087e12e2378 100644
--- a/explorer/testdata/returned_var/returned_var_omitted_expression.carbon
+++ b/explorer/testdata/returned_var/returned_var_omitted_expression.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/basic.carbon b/explorer/testdata/string/basic.carbon
index bdfc92c0a503..2c598952df93 100644
--- a/explorer/testdata/string/basic.carbon
+++ b/explorer/testdata/string/basic.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/block.carbon b/explorer/testdata/string/block.carbon
index 3896c18552b8..9755f11afffe 100644
--- a/explorer/testdata/string/block.carbon
+++ b/explorer/testdata/string/block.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/block_escaped_triple_quotes.carbon b/explorer/testdata/string/block_escaped_triple_quotes.carbon
index 9ea46d4fdf42..112cf460caae 100644
--- a/explorer/testdata/string/block_escaped_triple_quotes.carbon
+++ b/explorer/testdata/string/block_escaped_triple_quotes.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/block_file_type_indicator.carbon b/explorer/testdata/string/block_file_type_indicator.carbon
index 341addae6b3a..f30cfe03241f 100644
--- a/explorer/testdata/string/block_file_type_indicator.carbon
+++ b/explorer/testdata/string/block_file_type_indicator.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/fail_block_quotes_not_on_own_line.carbon b/explorer/testdata/string/fail_block_quotes_not_on_own_line.carbon
index cf4e2d98f2e0..2e3d4aea913d 100644
--- a/explorer/testdata/string/fail_block_quotes_not_on_own_line.carbon
+++ b/explorer/testdata/string/fail_block_quotes_not_on_own_line.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_block_quotes_not_on_own_line.carbon:[[@LINE+1]]: Invalid block string: Should end with triple quotes: error: closing """
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_block_quotes_not_on_own_line.carbon:[[@LINE+1]]: Invalid block string: Should end with triple quotes: error: closing """
   var s: String = """
     error: closing """ is not on its own line.
   """;
diff --git a/explorer/testdata/string/fail_hex_lower.carbon b/explorer/testdata/string/fail_hex_lower.carbon
index 77ce13270640..1bf1501eecd2 100644
--- a/explorer/testdata/string/fail_hex_lower.carbon
+++ b/explorer/testdata/string/fail_hex_lower.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_hex_lower.carbon:[[@LINE+1]]: Invalid escaping in string: "str\xaa"
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_hex_lower.carbon:[[@LINE+1]]: Invalid escaping in string: "str\xaa"
   Print("str\xaa");
   return 0;
 }
diff --git a/explorer/testdata/string/fail_hex_truncated.carbon b/explorer/testdata/string/fail_hex_truncated.carbon
index db532d87c583..196d09defec1 100644
--- a/explorer/testdata/string/fail_hex_truncated.carbon
+++ b/explorer/testdata/string/fail_hex_truncated.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_hex_truncated.carbon:[[@LINE+1]]: Invalid escaping in string: "str\x"
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_hex_truncated.carbon:[[@LINE+1]]: Invalid escaping in string: "str\x"
   Print("str\x");
   return 0;
 }
diff --git a/explorer/testdata/string/fail_invalid_escape.carbon b/explorer/testdata/string/fail_invalid_escape.carbon
index dad9bd663c8a..6326c1665e7c 100644
--- a/explorer/testdata/string/fail_invalid_escape.carbon
+++ b/explorer/testdata/string/fail_invalid_escape.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_invalid_escape.carbon:[[@LINE+1]]: Invalid escaping in string: "str\e"
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_invalid_escape.carbon:[[@LINE+1]]: Invalid escaping in string: "str\e"
   Print("str\e");
   return 0;
 }
diff --git a/explorer/testdata/string/fail_newline.carbon b/explorer/testdata/string/fail_newline.carbon
index 0c4657ad00e5..f5446d579944 100644
--- a/explorer/testdata/string/fail_newline.carbon
+++ b/explorer/testdata/string/fail_newline.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_newline.carbon:[[@LINE+2]]: missing closing quote in single-line string: "new
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_newline.carbon:[[@LINE+2]]: missing closing quote in single-line string: "new
   // CHECK-EMPTY:
   Print("new
 line");
diff --git a/explorer/testdata/string/fail_octal.carbon b/explorer/testdata/string/fail_octal.carbon
index 5ecb54f0df65..5500266a4377 100644
--- a/explorer/testdata/string/fail_octal.carbon
+++ b/explorer/testdata/string/fail_octal.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_octal.carbon:[[@LINE+1]]: Invalid escaping in string: "str\01"
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_octal.carbon:[[@LINE+1]]: Invalid escaping in string: "str\01"
   Print("str\01");
   return 0;
 }
diff --git a/explorer/testdata/string/fail_raw_block_more_hash_tags_on_left.carbon b/explorer/testdata/string/fail_raw_block_more_hash_tags_on_left.carbon
index 5ecd5defcc6f..f9c0fa7e36cd 100644
--- a/explorer/testdata/string/fail_raw_block_more_hash_tags_on_left.carbon
+++ b/explorer/testdata/string/fail_raw_block_more_hash_tags_on_left.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_block_more_hash_tags_on_left.carbon:[[@LINE+1]]: Unexpected end of file
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_block_more_hash_tags_on_left.carbon:[[@LINE+1]]: Unexpected end of file
   var s: String = ##"""
     error: there are more #s on the left than the right.
   """#;
diff --git a/explorer/testdata/string/fail_raw_block_more_hash_tags_on_right.carbon b/explorer/testdata/string/fail_raw_block_more_hash_tags_on_right.carbon
index 8575aee07ca7..3300c40b5827 100644
--- a/explorer/testdata/string/fail_raw_block_more_hash_tags_on_right.carbon
+++ b/explorer/testdata/string/fail_raw_block_more_hash_tags_on_right.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_block_more_hash_tags_on_right.carbon:[[@LINE+1]]: invalid character '\x23' in source file.
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_block_more_hash_tags_on_right.carbon:[[@LINE+1]]: invalid character '\x23' in source file.
   var s: String = #"""
     error: there are more #s on the right than the left.
   """##;
diff --git a/explorer/testdata/string/fail_raw_block_quotes_not_on_own_line.carbon b/explorer/testdata/string/fail_raw_block_quotes_not_on_own_line.carbon
index 245937c9fcd6..da754c84affc 100644
--- a/explorer/testdata/string/fail_raw_block_quotes_not_on_own_line.carbon
+++ b/explorer/testdata/string/fail_raw_block_quotes_not_on_own_line.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_block_quotes_not_on_own_line.carbon:[[@LINE+1]]: Invalid block string: Should end with triple quotes: error: closing """
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_block_quotes_not_on_own_line.carbon:[[@LINE+1]]: Invalid block string: Should end with triple quotes: error: closing """
   var s: String = #"""
     error: closing """# is not on its own line.
   """#;
diff --git a/explorer/testdata/string/fail_raw_block_single_line.carbon b/explorer/testdata/string/fail_raw_block_single_line.carbon
index a858b8a5debe..4a0a427cd84f 100644
--- a/explorer/testdata/string/fail_raw_block_single_line.carbon
+++ b/explorer/testdata/string/fail_raw_block_single_line.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn CompareStr(s: String) -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_block_single_line.carbon:[[@LINE+1]]: Invalid block string: Too few lines
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_block_single_line.carbon:[[@LINE+1]]: Invalid block string: Too few lines
   if (s == #"""raw string literal starting with """#) {
     return 0;
   }
diff --git a/explorer/testdata/string/fail_raw_more_hash_tags_on_left.carbon b/explorer/testdata/string/fail_raw_more_hash_tags_on_left.carbon
index 5013d8e6f5cc..3eb44ae759fd 100644
--- a/explorer/testdata/string/fail_raw_more_hash_tags_on_left.carbon
+++ b/explorer/testdata/string/fail_raw_more_hash_tags_on_left.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn CompareStr(s: String) -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_more_hash_tags_on_left.carbon:[[@LINE+2]]: missing closing quote in single-line string: ##"str"#) {
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_more_hash_tags_on_left.carbon:[[@LINE+2]]: missing closing quote in single-line string: ##"str"#) {
   // CHECK-EMPTY:
   if (s == ##"str"#) {
     return 0;
diff --git a/explorer/testdata/string/fail_raw_more_hash_tags_on_right.carbon b/explorer/testdata/string/fail_raw_more_hash_tags_on_right.carbon
index 669e9dea6ea0..deca2950e19a 100644
--- a/explorer/testdata/string/fail_raw_more_hash_tags_on_right.carbon
+++ b/explorer/testdata/string/fail_raw_more_hash_tags_on_right.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn CompareStr(s: String) -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_more_hash_tags_on_right.carbon:[[@LINE+1]]: invalid character '\x23' in source file.
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_raw_more_hash_tags_on_right.carbon:[[@LINE+1]]: invalid character '\x23' in source file.
   if (s == "str"#) {
     return 0;
   }
diff --git a/explorer/testdata/string/fail_tab.carbon b/explorer/testdata/string/fail_tab.carbon
index 9ec19fddb8da..bf71e9c5f629 100644
--- a/explorer/testdata/string/fail_tab.carbon
+++ b/explorer/testdata/string/fail_tab.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_tab.carbon:[[@LINE+1]]: Invalid escaping in string: "new	line"
+  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/string/fail_tab.carbon:[[@LINE+1]]: Invalid escaping in string: "new	line"
   Print("new	line");
   return 0;
 }
diff --git a/explorer/testdata/string/hex.carbon b/explorer/testdata/string/hex.carbon
index 173edd6a8619..d94474b364b3 100644
--- a/explorer/testdata/string/hex.carbon
+++ b/explorer/testdata/string/hex.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/newline.carbon b/explorer/testdata/string/newline.carbon
index 3762a73072b7..27f0f6fec070 100644
--- a/explorer/testdata/string/newline.carbon
+++ b/explorer/testdata/string/newline.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/raw_basic.carbon b/explorer/testdata/string/raw_basic.carbon
index 2749ada7719f..0c33d1bcce2a 100644
--- a/explorer/testdata/string/raw_basic.carbon
+++ b/explorer/testdata/string/raw_basic.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/raw_basic_multi_hashtag.carbon b/explorer/testdata/string/raw_basic_multi_hashtag.carbon
index 9cbe6c608d94..7a508c74c633 100644
--- a/explorer/testdata/string/raw_basic_multi_hashtag.carbon
+++ b/explorer/testdata/string/raw_basic_multi_hashtag.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/raw_block.carbon b/explorer/testdata/string/raw_block.carbon
index fd19c490c437..4b12eb2460f0 100644
--- a/explorer/testdata/string/raw_block.carbon
+++ b/explorer/testdata/string/raw_block.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/raw_block_escaped_back_slash.carbon b/explorer/testdata/string/raw_block_escaped_back_slash.carbon
index f22a71636f89..76eaf4ff268e 100644
--- a/explorer/testdata/string/raw_block_escaped_back_slash.carbon
+++ b/explorer/testdata/string/raw_block_escaped_back_slash.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/raw_block_escaped_triple_quotes.carbon b/explorer/testdata/string/raw_block_escaped_triple_quotes.carbon
index 53d2306a3db1..9da98e9efccf 100644
--- a/explorer/testdata/string/raw_block_escaped_triple_quotes.carbon
+++ b/explorer/testdata/string/raw_block_escaped_triple_quotes.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/raw_nesting.carbon b/explorer/testdata/string/raw_nesting.carbon
index 054e4a622c15..eefec8b29007 100644
--- a/explorer/testdata/string/raw_nesting.carbon
+++ b/explorer/testdata/string/raw_nesting.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/string/unicode.carbon b/explorer/testdata/string/unicode.carbon
index d4cd296e3a4f..7c8c0113aac5 100644
--- a/explorer/testdata/string/unicode.carbon
+++ b/explorer/testdata/string/unicode.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/struct/assign.carbon b/explorer/testdata/struct/assign.carbon
index 113c2746489f..00894ce9bd5b 100644
--- a/explorer/testdata/struct/assign.carbon
+++ b/explorer/testdata/struct/assign.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/struct/assign_member.carbon b/explorer/testdata/struct/assign_member.carbon
index f0768b476a14..77c6dd6d4fc1 100644
--- a/explorer/testdata/struct/assign_member.carbon
+++ b/explorer/testdata/struct/assign_member.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/struct/empty.carbon b/explorer/testdata/struct/empty.carbon
index 658c7eb8ef58..9254e06850d1 100644
--- a/explorer/testdata/struct/empty.carbon
+++ b/explorer/testdata/struct/empty.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/struct/ending_comma.carbon b/explorer/testdata/struct/ending_comma.carbon
index 72b4830507ba..0a5e1544f5ca 100644
--- a/explorer/testdata/struct/ending_comma.carbon
+++ b/explorer/testdata/struct/ending_comma.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/struct/equality.carbon b/explorer/testdata/struct/equality.carbon
index cfee857cdd81..5cbb5111b03d 100644
--- a/explorer/testdata/struct/equality.carbon
+++ b/explorer/testdata/struct/equality.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: t1 == t2: 1
-// CHECK: t1 != t2: 0
-// CHECK: result: 0
+// CHECK:t1 == t2: 1
+// CHECK:t1 != t2: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/struct/equality_false.carbon b/explorer/testdata/struct/equality_false.carbon
index 7146e053295c..d6bc27076802 100644
--- a/explorer/testdata/struct/equality_false.carbon
+++ b/explorer/testdata/struct/equality_false.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/struct/fail_equality_type.carbon b/explorer/testdata/struct/fail_equality_type.carbon
index 8dbbd0438ffd..aeec008cff7c 100644
--- a/explorer/testdata/struct/fail_equality_type.carbon
+++ b/explorer/testdata/struct/fail_equality_type.carbon
@@ -2,7 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 2>&1 | %{FileCheck} %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -20,7 +21,7 @@ external impl {.x: i32, .y: i32} as EqWith(Self) {
 fn Main() -> i32 {
   var t1: {.x: i32, .y: i32} = {.x = 5, .y = 2};
   var t2: {.x: i32,} = {.x = 5,};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/struct/fail_equality_type.carbon:[[@LINE+1]]: {.x: i32, .y: i32} is not equality comparable with {.x: i32} (could not find implementation of interface EqWith(U = {.x: i32}) for {.x: i32, .y: i32})
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/struct/fail_equality_type.carbon:[[@LINE+1]]: {.x: i32, .y: i32} is not equality comparable with {.x: i32} (could not find implementation of interface EqWith(U = {.x: i32}) for {.x: i32, .y: i32})
   if (t1 == t2) {
     return 1;
   } else {
diff --git a/explorer/testdata/struct/fail_field_access_mismatch.carbon b/explorer/testdata/struct/fail_field_access_mismatch.carbon
index 67eba881dfad..1c6fecf57d8a 100644
--- a/explorer/testdata/struct/fail_field_access_mismatch.carbon
+++ b/explorer/testdata/struct/fail_field_access_mismatch.carbon
@@ -2,15 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/struct/fail_field_access_mismatch.carbon:[[@LINE+1]]: struct {.x: i32, .y: i32} does not have a field named z
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/struct/fail_field_access_mismatch.carbon:[[@LINE+1]]: struct {.x: i32, .y: i32} does not have a field named z
   return {.x = 1, .y = 2}.z - 1;
 }
diff --git a/explorer/testdata/struct/name_order.carbon b/explorer/testdata/struct/name_order.carbon
index 2535bcaa13d7..420903be6422 100644
--- a/explorer/testdata/struct/name_order.carbon
+++ b/explorer/testdata/struct/name_order.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/struct/temp.carbon b/explorer/testdata/struct/temp.carbon
index c12cfdcd02c5..773d8162a237 100644
--- a/explorer/testdata/struct/temp.carbon
+++ b/explorer/testdata/struct/temp.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/struct/var.carbon b/explorer/testdata/struct/var.carbon
index 49b66a53f819..35fd41a84edb 100644
--- a/explorer/testdata/struct/var.carbon
+++ b/explorer/testdata/struct/var.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/tuple/ending_comma.carbon b/explorer/testdata/tuple/ending_comma.carbon
index 5182b347212c..d560804befc2 100644
--- a/explorer/testdata/tuple/ending_comma.carbon
+++ b/explorer/testdata/tuple/ending_comma.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/tuple/equality.carbon b/explorer/testdata/tuple/equality.carbon
index 5d6da7823507..a9b06b23708d 100644
--- a/explorer/testdata/tuple/equality.carbon
+++ b/explorer/testdata/tuple/equality.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/tuple/equality_false.carbon b/explorer/testdata/tuple/equality_false.carbon
index f441d27458b2..ac7f577d1b19 100644
--- a/explorer/testdata/tuple/equality_false.carbon
+++ b/explorer/testdata/tuple/equality_false.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/tuple/fail_equality_type.carbon b/explorer/testdata/tuple/fail_equality_type.carbon
index ca36dd98a74f..f92c75d5bc73 100644
--- a/explorer/testdata/tuple/fail_equality_type.carbon
+++ b/explorer/testdata/tuple/fail_equality_type.carbon
@@ -2,7 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 2>&1 | %{FileCheck} %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -10,7 +11,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var t1: (i32, i32) = (5, 2);
   var t2: (i32,) = (5,);
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/tuple/fail_equality_type.carbon:[[@LINE+1]]: (i32, i32) is not equality comparable with (i32) (could not find implementation of interface EqWith(U = (i32)) for (i32, i32))
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/tuple/fail_equality_type.carbon:[[@LINE+1]]: (i32, i32) is not equality comparable with (i32) (could not find implementation of interface EqWith(U = (i32)) for (i32, i32))
   if (t1 == t2) {
     return 1;
   } else {
diff --git a/explorer/testdata/tuple/fail_index.carbon b/explorer/testdata/tuple/fail_index.carbon
index fa0ef77faf77..d9267d25c667 100644
--- a/explorer/testdata/tuple/fail_index.carbon
+++ b/explorer/testdata/tuple/fail_index.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: auto = (0, 1);
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/tuple/fail_index.carbon:[[@LINE+1]]: index 2 is out of range for type (i32, i32)
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/tuple/fail_index.carbon:[[@LINE+1]]: index 2 is out of range for type (i32, i32)
   return x[2];
 }
diff --git a/explorer/testdata/tuple/fail_index_var.carbon b/explorer/testdata/tuple/fail_index_var.carbon
index 31c86765d248..fcf97a325ff7 100644
--- a/explorer/testdata/tuple/fail_index_var.carbon
+++ b/explorer/testdata/tuple/fail_index_var.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,6 +11,6 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: auto = (0, 1);
   var index: i32 = 0;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/tuple/fail_index_var.carbon:[[@LINE+1]]: could not find `index: i32`
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/tuple/fail_index_var.carbon:[[@LINE+1]]: could not find `index: i32`
   return x[index];
 }
diff --git a/explorer/testdata/tuple/fail_to_array.carbon b/explorer/testdata/tuple/fail_to_array.carbon
index 97c055b69b7b..436f6d6151c6 100644
--- a/explorer/testdata/tuple/fail_to_array.carbon
+++ b/explorer/testdata/tuple/fail_to_array.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var t: auto = (1, 2);
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/tuple/fail_to_array.carbon:[[@LINE+1]]: type error in name binding: '(i32, i32)' is not implicitly convertible to '[i32; 3]'
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/tuple/fail_to_array.carbon:[[@LINE+1]]: type error in name binding: '(i32, i32)' is not implicitly convertible to '[i32; 3]'
   var a: [i32; 3] = t;
 }
diff --git a/explorer/testdata/tuple/index.carbon b/explorer/testdata/tuple/index.carbon
index c0b9b7e3017e..ec0571ce6c2c 100644
--- a/explorer/testdata/tuple/index.carbon
+++ b/explorer/testdata/tuple/index.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/tuple/match.carbon b/explorer/testdata/tuple/match.carbon
index 5744c60a72d0..e9d9ad446661 100644
--- a/explorer/testdata/tuple/match.carbon
+++ b/explorer/testdata/tuple/match.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/tuple/match_nested.carbon b/explorer/testdata/tuple/match_nested.carbon
index d557a0b672ef..04892b4c5aed 100644
--- a/explorer/testdata/tuple/match_nested.carbon
+++ b/explorer/testdata/tuple/match_nested.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/tuple/no_ending_comma.carbon b/explorer/testdata/tuple/no_ending_comma.carbon
index 0058f95ef6fc..c8c66cfc1f25 100644
--- a/explorer/testdata/tuple/no_ending_comma.carbon
+++ b/explorer/testdata/tuple/no_ending_comma.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/tuple/to_array.carbon b/explorer/testdata/tuple/to_array.carbon
index 250b3ec31bca..d7c95fa7ac76 100644
--- a/explorer/testdata/tuple/to_array.carbon
+++ b/explorer/testdata/tuple/to_array.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 3
+// CHECK:result: 3
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/control_flow_defer_to_dynamic.carbon b/explorer/testdata/unformed/control_flow_defer_to_dynamic.carbon
index 8c27b6f79969..a02d5b40933f 100644
--- a/explorer/testdata/unformed/control_flow_defer_to_dynamic.carbon
+++ b/explorer/testdata/unformed/control_flow_defer_to_dynamic.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/dynamic/fail_global.carbon b/explorer/testdata/unformed/dynamic/fail_global.carbon
index 49e6eed20958..1918c7ab3165 100644
--- a/explorer/testdata/unformed/dynamic/fail_global.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_global.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,6 +11,6 @@ package ExplorerTest api;
 var x: i32;
 
 fn Main() -> i32 {
-  // CHECK: RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_global.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_global.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
   return x;
 }
diff --git a/explorer/testdata/unformed/dynamic/fail_param.carbon b/explorer/testdata/unformed/dynamic/fail_param.carbon
index 865e921dcb93..8f37ffd5e05c 100644
--- a/explorer/testdata/unformed/dynamic/fail_param.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_param.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -20,6 +18,6 @@ fn Main() -> i32 {
     x = 0;
   }
   // Static analysis thinks `x` may be formed, defer the check to run-time.
-  // CHECK: RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_param.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_param.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
   return AddInt(x, 2);
 }
diff --git a/explorer/testdata/unformed/dynamic/fail_pattern_declare.carbon b/explorer/testdata/unformed/dynamic/fail_pattern_declare.carbon
index f72cc8605199..f9220d702ab8 100644
--- a/explorer/testdata/unformed/dynamic/fail_pattern_declare.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_pattern_declare.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -17,6 +15,6 @@ fn Main() -> i32 {
     y = 0;
   }
   // Static analysis thinks `y` may be formed, defer the check to run-time.
-  // CHECK: RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_pattern_declare.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<y>>
+  // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_pattern_declare.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<y>>
   return y;
 }
diff --git a/explorer/testdata/unformed/dynamic/fail_return.carbon b/explorer/testdata/unformed/dynamic/fail_return.carbon
index 499d47c6eeaa..c91452716973 100644
--- a/explorer/testdata/unformed/dynamic/fail_return.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_return.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,6 +14,6 @@ fn Main() -> i32 {
     x = 0;
   }
   // Static analysis thinks `x` may be formed, defer the check to run-time.
-  // CHECK: RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_return.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_return.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
   return x;
 }
diff --git a/explorer/testdata/unformed/dynamic/fail_returned_var.carbon b/explorer/testdata/unformed/dynamic/fail_returned_var.carbon
index e83995cc2ca2..a1962aa3b542 100644
--- a/explorer/testdata/unformed/dynamic/fail_returned_var.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_returned_var.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,6 +14,6 @@ fn Main() -> i32 {
     x = 0;
   }
   // Static analysis thinks `x` may be formed, defer the check to run-time.
-  // CHECK: RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_returned_var.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_returned_var.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
   return var;
 }
diff --git a/explorer/testdata/unformed/dynamic/fail_rhs_assign.carbon b/explorer/testdata/unformed/dynamic/fail_rhs_assign.carbon
index 39761c33c4e3..8c53f694b4b8 100644
--- a/explorer/testdata/unformed/dynamic/fail_rhs_assign.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_rhs_assign.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -17,7 +15,7 @@ fn Main() -> i32 {
     x = 0;
   }
   // Static analysis thinks `x` may be formed, defer the check to run-time.
-  // CHECK: RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_rhs_assign.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/unformed/dynamic/fail_rhs_assign.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
   y = x;
   return y;
 }
diff --git a/explorer/testdata/unformed/global_assign_before_use.carbon b/explorer/testdata/unformed/global_assign_before_use.carbon
index 561e842ba908..0626bd56368b 100644
--- a/explorer/testdata/unformed/global_assign_before_use.carbon
+++ b/explorer/testdata/unformed/global_assign_before_use.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/global_escape.carbon b/explorer/testdata/unformed/global_escape.carbon
index 8acbb6ed9e27..1175ec1778f8 100644
--- a/explorer/testdata/unformed/global_escape.carbon
+++ b/explorer/testdata/unformed/global_escape.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 42
+// CHECK:result: 42
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/global_unformed_without_use.carbon b/explorer/testdata/unformed/global_unformed_without_use.carbon
index 8d334acdfea5..cdd0cea1f1fb 100644
--- a/explorer/testdata/unformed/global_unformed_without_use.carbon
+++ b/explorer/testdata/unformed/global_unformed_without_use.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/local_assign_before_use.carbon b/explorer/testdata/unformed/local_assign_before_use.carbon
index f5e9d9592e55..39100eb60d17 100644
--- a/explorer/testdata/unformed/local_assign_before_use.carbon
+++ b/explorer/testdata/unformed/local_assign_before_use.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/local_escape.carbon b/explorer/testdata/unformed/local_escape.carbon
index 699d54a547ef..29ea8ba0580b 100644
--- a/explorer/testdata/unformed/local_escape.carbon
+++ b/explorer/testdata/unformed/local_escape.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 42
+// CHECK:result: 42
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/local_unformed_without_use.carbon b/explorer/testdata/unformed/local_unformed_without_use.carbon
index a4f69675a5ef..0c96fdafcc88 100644
--- a/explorer/testdata/unformed/local_unformed_without_use.carbon
+++ b/explorer/testdata/unformed/local_unformed_without_use.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/pattern_declare.carbon b/explorer/testdata/unformed/pattern_declare.carbon
index 19311799c736..496ec6d8e520 100644
--- a/explorer/testdata/unformed/pattern_declare.carbon
+++ b/explorer/testdata/unformed/pattern_declare.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/returned_var_assign_before_use.carbon b/explorer/testdata/unformed/returned_var_assign_before_use.carbon
index 585bed71ff8e..83f4677b2beb 100644
--- a/explorer/testdata/unformed/returned_var_assign_before_use.carbon
+++ b/explorer/testdata/unformed/returned_var_assign_before_use.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 1
+// CHECK:result: 1
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/unformed/static/fail_field_value.carbon b/explorer/testdata/unformed/static/fail_field_value.carbon
index e30c47ca17f0..7d8df13dae40 100644
--- a/explorer/testdata/unformed/static/fail_field_value.carbon
+++ b/explorer/testdata/unformed/static/fail_field_value.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_field_value.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_field_value.carbon:[[@LINE+1]]: use of uninitialized variable x
   var p: auto = {.x = x,};
   return 0;
 }
diff --git a/explorer/testdata/unformed/static/fail_if_cond.carbon b/explorer/testdata/unformed/static/fail_if_cond.carbon
index 41a87960a56e..12d1193b0a30 100644
--- a/explorer/testdata/unformed/static/fail_if_cond.carbon
+++ b/explorer/testdata/unformed/static/fail_if_cond.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_if_cond.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_if_cond.carbon:[[@LINE+1]]: use of uninitialized variable x
   if (x == 0) {
     return 0;
   }
diff --git a/explorer/testdata/unformed/static/fail_if_else.carbon b/explorer/testdata/unformed/static/fail_if_else.carbon
index 5374c92ff372..04a4cd4e1f95 100644
--- a/explorer/testdata/unformed/static/fail_if_else.carbon
+++ b/explorer/testdata/unformed/static/fail_if_else.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -17,7 +15,7 @@ fn Main() -> i32 {
   if (Foo() == 0) {
     return 0;
   } else {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_if_else.carbon:[[@LINE+1]]: use of uninitialized variable x
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_if_else.carbon:[[@LINE+1]]: use of uninitialized variable x
     return x;
   }
 }
diff --git a/explorer/testdata/unformed/static/fail_if_then.carbon b/explorer/testdata/unformed/static/fail_if_then.carbon
index 063494008c1b..af9258da65fe 100644
--- a/explorer/testdata/unformed/static/fail_if_then.carbon
+++ b/explorer/testdata/unformed/static/fail_if_then.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,7 +13,7 @@ fn Foo() -> i32;
 fn Main() -> i32 {
   var x: i32;
   if (Foo() == 0) {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_if_then.carbon:[[@LINE+1]]: use of uninitialized variable x
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_if_then.carbon:[[@LINE+1]]: use of uninitialized variable x
     return x;
   }
   return 1;
diff --git a/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon b/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon
index 214919bdf134..81d9477ff4b4 100644
--- a/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon
+++ b/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,6 +11,6 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var (x: i32, y: i32);
   x = 1;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon:[[@LINE+1]]: use of uninitialized variable y
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon:[[@LINE+1]]: use of uninitialized variable y
   return y;
 }
diff --git a/explorer/testdata/unformed/static/fail_local_rhs_assign.carbon b/explorer/testdata/unformed/static/fail_local_rhs_assign.carbon
index 099d581f1474..c7ab8e006cab 100644
--- a/explorer/testdata/unformed/static/fail_local_rhs_assign.carbon
+++ b/explorer/testdata/unformed/static/fail_local_rhs_assign.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +11,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: i32;
   var y: i32;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_local_rhs_assign.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_local_rhs_assign.carbon:[[@LINE+1]]: use of uninitialized variable x
   y = x;
   return y;
 }
diff --git a/explorer/testdata/unformed/static/fail_match_clause.carbon b/explorer/testdata/unformed/static/fail_match_clause.carbon
index 5813f605f111..213b19a62e4c 100644
--- a/explorer/testdata/unformed/static/fail_match_clause.carbon
+++ b/explorer/testdata/unformed/static/fail_match_clause.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -19,7 +17,7 @@ fn Main() -> i32 {
       return 2;
     }
     case 1 => {
-      // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_match_clause.carbon:[[@LINE+1]]: use of uninitialized variable x
+      // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_match_clause.carbon:[[@LINE+1]]: use of uninitialized variable x
       return x;
     }
     default => {
diff --git a/explorer/testdata/unformed/static/fail_match_expression.carbon b/explorer/testdata/unformed/static/fail_match_expression.carbon
index dd449ad548b5..6fd85fb39d3f 100644
--- a/explorer/testdata/unformed/static/fail_match_expression.carbon
+++ b/explorer/testdata/unformed/static/fail_match_expression.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x : i32;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_match_expression.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_match_expression.carbon:[[@LINE+1]]: use of uninitialized variable x
   match (x) {
     case 0 => {
       return 1;
diff --git a/explorer/testdata/unformed/static/fail_param.carbon b/explorer/testdata/unformed/static/fail_param.carbon
index eac6e7dfac96..4eabadec7ab7 100644
--- a/explorer/testdata/unformed/static/fail_param.carbon
+++ b/explorer/testdata/unformed/static/fail_param.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,6 +14,6 @@ fn AddInt(a: i32, b: i32) -> auto {
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_param.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_param.carbon:[[@LINE+1]]: use of uninitialized variable x
   return AddInt(x, 2);
 }
diff --git a/explorer/testdata/unformed/static/fail_return.carbon b/explorer/testdata/unformed/static/fail_return.carbon
index 3a2f5a0b03ef..b872e2257dfb 100644
--- a/explorer/testdata/unformed/static/fail_return.carbon
+++ b/explorer/testdata/unformed/static/fail_return.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_return.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_return.carbon:[[@LINE+1]]: use of uninitialized variable x
   return x;
 }
diff --git a/explorer/testdata/unformed/static/fail_returned_var.carbon b/explorer/testdata/unformed/static/fail_returned_var.carbon
index 6d42d83e8831..dae83edcca1f 100644
--- a/explorer/testdata/unformed/static/fail_returned_var.carbon
+++ b/explorer/testdata/unformed/static/fail_returned_var.carbon
@@ -2,16 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   returned var x: i32;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_returned_var.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_returned_var.carbon:[[@LINE+1]]: use of uninitialized variable x
   return var;
 }
diff --git a/explorer/testdata/unformed/static/fail_rhs_def.carbon b/explorer/testdata/unformed/static/fail_rhs_def.carbon
index 274c2943249e..463009fac440 100644
--- a/explorer/testdata/unformed/static/fail_rhs_def.carbon
+++ b/explorer/testdata/unformed/static/fail_rhs_def.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_rhs_def.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_rhs_def.carbon:[[@LINE+1]]: use of uninitialized variable x
   var y: i32 = x;
   return x;
 }
diff --git a/explorer/testdata/unformed/static/fail_struct_member_access.carbon b/explorer/testdata/unformed/static/fail_struct_member_access.carbon
index 0d8b42f1be1e..6587c9ad65af 100644
--- a/explorer/testdata/unformed/static/fail_struct_member_access.carbon
+++ b/explorer/testdata/unformed/static/fail_struct_member_access.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var p: {.x: i32, .y: i32};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_struct_member_access.carbon:[[@LINE+1]]: use of uninitialized variable p
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_struct_member_access.carbon:[[@LINE+1]]: use of uninitialized variable p
   p.x = p.y;
   return 0;
 }
diff --git a/explorer/testdata/unformed/static/fail_while_body.carbon b/explorer/testdata/unformed/static/fail_while_body.carbon
index 40025f99e85c..d66d70986676 100644
--- a/explorer/testdata/unformed/static/fail_while_body.carbon
+++ b/explorer/testdata/unformed/static/fail_while_body.carbon
@@ -2,10 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,7 +13,7 @@ fn Foo() -> i32;
 fn Main() -> i32 {
   var (x: i32, y: i32);
   while (Foo() == 0) {
-    // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_while_body.carbon:[[@LINE+1]]: use of uninitialized variable x
+    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_while_body.carbon:[[@LINE+1]]: use of uninitialized variable x
     y = x;
   }
   return 1;
diff --git a/explorer/testdata/unformed/static/fail_while_cond.carbon b/explorer/testdata/unformed/static/fail_while_cond.carbon
index f34c3f0dd1fd..5711ef2651bc 100644
--- a/explorer/testdata/unformed/static/fail_while_cond.carbon
+++ b/explorer/testdata/unformed/static/fail_while_cond.carbon
@@ -2,17 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{not} %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var (x: i32, y: i32);
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_while_cond.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/unformed/static/fail_while_cond.carbon:[[@LINE+1]]: use of uninitialized variable x
   while (x == 0) {
     y = 1;
   }
diff --git a/explorer/testdata/while/basic.carbon b/explorer/testdata/while/basic.carbon
index d3166fa2b8c2..12c89e4dbaba 100644
--- a/explorer/testdata/while/basic.carbon
+++ b/explorer/testdata/while/basic.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/while/break.carbon b/explorer/testdata/while/break.carbon
index 285f613ab7dd..402fc8ebd522 100644
--- a/explorer/testdata/while/break.carbon
+++ b/explorer/testdata/while/break.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/while/continue.carbon b/explorer/testdata/while/continue.carbon
index d92a066c884b..1b57e7060db0 100644
--- a/explorer/testdata/while/continue.carbon
+++ b/explorer/testdata/while/continue.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/while/convert_condition.carbon b/explorer/testdata/while/convert_condition.carbon
index 30218d99dbc9..9ee13ae871b2 100644
--- a/explorer/testdata/while/convert_condition.carbon
+++ b/explorer/testdata/while/convert_condition.carbon
@@ -2,12 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
-// RUN: %{explorer} --parser_debug --trace_file=- %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes %s
+// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK: result: 0
+// CHECK:result: 0
 
 package ExplorerTest api;
 
diff --git a/explorer/update_checks.py b/explorer/update_checks.py
index 26dcb0476d8c..7100b1e6ba3d 100755
--- a/explorer/update_checks.py
+++ b/explorer/update_checks.py
@@ -93,7 +93,7 @@ class SimpleCheckLine(CheckLine):
 
     def format(self, **kwargs: Any) -> str:
         if self.expected:
-            return f"{self.indent}// CHECK: {self.expected}\n"
+            return f"{self.indent}// CHECK:{self.expected}\n"
         else:
             return f"{self.indent}// CHECK-EMPTY:\n"
 
@@ -118,7 +118,7 @@ class CheckLineWithLineNumber(CheckLine):
         delta = line_number_remap[self.line_number] - output_line_number
         # We use `:+d` here to produce `LINE-n` or `LINE+n` as appropriate.
         return (
-            f"{self.indent}// CHECK: {self.before}[[@LINE{delta:+d}]]"
+            f"{self.indent}// CHECK:{self.before}[[@LINE{delta:+d}]]"
             + f"{self.after}\n"
         )
 
diff --git a/toolchain/driver/testdata/carbon_test.carbon b/toolchain/driver/testdata/carbon_test.carbon
index 415263c2b5c6..1ab7e1cc7116 100644
--- a/toolchain/driver/testdata/carbon_test.carbon
+++ b/toolchain/driver/testdata/carbon_test.carbon
@@ -2,22 +2,20 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{carbon} dump tokens %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
+// RUN: %{carbon} dump tokens %s 2>&1 | %{FileCheck-strict} %s
 
+// CHECK:token: { index:  0, kind:              'Fn', line: {{ *}}[[@LINE+7]], column:   1, indent: 1, spelling: 'fn', has_trailing_space: true }
+// CHECK:token: { index:  1, kind:      'Identifier', line: {{ *}}[[@LINE+6]], column:   4, indent: 1, spelling: 'run', identifier: 0 }
+// CHECK:token: { index:  2, kind:       'OpenParen', line: {{ *}}[[@LINE+5]], column:   7, indent: 1, spelling: '(', closing_token: 5 }
+// CHECK:token: { index:  3, kind:      'Identifier', line: {{ *}}[[@LINE+4]], column:   8, indent: 1, spelling: 'String', identifier: 1, has_trailing_space: true }
+// CHECK:token: { index:  4, kind:      'Identifier', line: {{ *}}[[@LINE+3]], column:  15, indent: 1, spelling: 'program', identifier: 2 }
+// CHECK:token: { index:  5, kind:      'CloseParen', line: {{ *}}[[@LINE+2]], column:  22, indent: 1, spelling: ')', opening_token: 2, has_trailing_space: true }
+// CHECK:token: { index:  6, kind:  'OpenCurlyBrace', line: {{ *}}[[@LINE+1]], column:  24, indent: 1, spelling: '{', closing_token: 10, has_trailing_space: true }
 fn run(String program) {
+  // CHECK:token: { index:  7, kind:          'Return', line: {{ *}}[[@LINE+3]], column:   3, indent: 3, spelling: 'return', has_trailing_space: true }
+  // CHECK:token: { index:  8, kind:      'Identifier', line: {{ *}}[[@LINE+2]], column:  10, indent: 3, spelling: 'True', identifier: 3 }
+  // CHECK:token: { index:  9, kind:            'Semi', line: {{ *}}[[@LINE+1]], column:  14, indent: 3, spelling: ';', has_trailing_space: true }
   return True;
+// CHECK:token: { index: 10, kind: 'CloseCurlyBrace', line: {{ *}}[[@LINE+1]], column:   1, indent: 1, spelling: '}', opening_token: 6, has_trailing_space: true }
 }
-
-// CHECK: token: { index:  0, kind:              'Fn', line: 8, column:   1, indent: 1, spelling: 'fn', has_trailing_space: true }
-// CHECK: token: { index:  1, kind:      'Identifier', line: 8, column:   4, indent: 1, spelling: 'run', identifier: 0 }
-// CHECK: token: { index:  2, kind:       'OpenParen', line: 8, column:   7, indent: 1, spelling: '(', closing_token: 5 }
-// CHECK: token: { index:  3, kind:      'Identifier', line: 8, column:   8, indent: 1, spelling: 'String', identifier: 1, has_trailing_space: true }
-// CHECK: token: { index:  4, kind:      'Identifier', line: 8, column:  15, indent: 1, spelling: 'program', identifier: 2 }
-// CHECK: token: { index:  5, kind:      'CloseParen', line: 8, column:  22, indent: 1, spelling: ')', opening_token: 2, has_trailing_space: true }
-// CHECK: token: { index:  6, kind:  'OpenCurlyBrace', line: 8, column:  24, indent: 1, spelling: '{', closing_token: 10, has_trailing_space: true }
-// CHECK: token: { index:  7, kind:          'Return', line: 9, column:   3, indent: 3, spelling: 'return', has_trailing_space: true }
-// CHECK: token: { index:  8, kind:      'Identifier', line: 9, column:  10, indent: 3, spelling: 'True', identifier: 3 }
-// CHECK: token: { index:  9, kind:            'Semi', line: 9, column:  14, indent: 3, spelling: ';', has_trailing_space: true }
-// CHECK: token: { index: 10, kind: 'CloseCurlyBrace', line: 10, column:   1, indent: 1, spelling: '}', opening_token: 6, has_trailing_space: true }
-// CHECK: token: { index: 11, kind:       'EndOfFile', line: 23, column: 104, indent: 1, spelling: '' }
+// CHECK:token: { index: 11, kind:       'EndOfFile', line: {{ *}}[[@LINE]], column: {{[0-9]+}}, indent: 1, spelling: '' }
diff --git a/toolchain/driver/testdata/errors_sorted_test.carbon b/toolchain/driver/testdata/errors_sorted_test.carbon
index 11360c0dd6c5..cf76cc2a4181 100644
--- a/toolchain/driver/testdata/errors_sorted_test.carbon
+++ b/toolchain/driver/testdata/errors_sorted_test.carbon
@@ -2,14 +2,12 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{carbon} dump tokens %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
+// RUN: %{not} %{carbon} dump tokens %s 2>&1 | %{FileCheck-strict} %s
 
+// CHECK:{{.*}}/errors_sorted_test.carbon:[[@LINE+1]]:24: Closing symbol does not match most recent opening symbol.
 fn run(String program) {
   return True;
 
+// CHECK:{{.*}}/errors_sorted_test.carbon:[[@LINE+1]]:10: Invalid digit 'a' in decimal numeric literal.
 var x = 3a;
-
-// CHECK: {{.*}}/errors_sorted_test.carbon:8:24: Closing symbol does not match most recent opening symbol.
-// CHECK: {{.*}}/errors_sorted_test.carbon:11:10: Invalid digit 'a' in decimal numeric literal.
-// CHECK-COUNT-17: token: {{.*}}
+// CHECK-COUNT-17:token: {{.*}}
diff --git a/toolchain/driver/testdata/errors_streamed_test.carbon b/toolchain/driver/testdata/errors_streamed_test.carbon
index 340c819d8a17..040ad8cf24f4 100644
--- a/toolchain/driver/testdata/errors_streamed_test.carbon
+++ b/toolchain/driver/testdata/errors_streamed_test.carbon
@@ -3,13 +3,13 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // RUN: %{not} %{carbon} --print-errors=streamed dump tokens %s 2>&1 | \
-// RUN:   %{FileCheck} --match-full-lines --allow-unused-prefixes=false %s
+// RUN:   %{FileCheck-strict} %s
 
 fn run(String program) {
   return True;
 
 var x = 3a;
 
-// CHECK: {{.*}}/errors_streamed_test.carbon:11:10: Invalid digit 'a' in decimal numeric literal.
-// CHECK: {{.*}}/errors_streamed_test.carbon:8:24: Closing symbol does not match most recent opening symbol.
-// CHECK-COUNT-17: token: {{.*}}
+// CHECK:{{.*}}/errors_streamed_test.carbon:[[@LINE-2]]:10: Invalid digit 'a' in decimal numeric literal.
+// CHECK:{{.*}}/errors_streamed_test.carbon:[[@LINE-6]]:24: Closing symbol does not match most recent opening symbol.
+// CHECK-COUNT-17:token: {{.*}}
diff --git a/toolchain/driver/testdata/lit.cfg.py b/toolchain/driver/testdata/lit.cfg.py
deleted file mode 100644
index e975c265d658..000000000000
--- a/toolchain/driver/testdata/lit.cfg.py
+++ /dev/null
@@ -1,35 +0,0 @@
-__copyright__ = """
-Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-Exceptions. See /LICENSE for license information.
-SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-"""
-
-import lit.formats
-import os
-
-
-# This is a provided variable, ignore the undefined name warning.
-config = config  # noqa: F821
-
-
-def fullpath(relative_path):
-    return os.path.join(os.environ["TEST_SRCDIR"], relative_path)
-
-
-config.name = "lit"
-config.suffixes = [".carbon"]
-config.test_format = lit.formats.ShTest()
-
-config.substitutions.append(
-    (
-        "%{carbon}",
-        fullpath("carbon/toolchain/driver/carbon"),
-    )
-)
-config.substitutions.append(("%{not}", fullpath("llvm-project/llvm/not")))
-config.substitutions.append(
-    (
-        "%{FileCheck}",
-        fullpath("llvm-project/llvm/FileCheck --dump-input-filter=all"),
-    )
-)
diff --git a/toolchain/driver/testdata/lit.cfg.py b/toolchain/driver/testdata/lit.cfg.py
new file mode 120000
index 000000000000..c323f8a5e8da
--- /dev/null
+++ b/toolchain/driver/testdata/lit.cfg.py
@@ -0,0 +1 @@
+../../../bazel/testing/lit.cfg.py
\ No newline at end of file
diff --git a/toolchain/semantics/testdata/empty.carbon b/toolchain/semantics/testdata/empty.carbon
index 5aac04177ef9..3e30c0bf745c 100644
--- a/toolchain/semantics/testdata/empty.carbon
+++ b/toolchain/semantics/testdata/empty.carbon
@@ -2,6 +2,6 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheckStrict} %s
+// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheck-strict} %s
 // CHECK:{
 // CHECK:}
diff --git a/toolchain/semantics/testdata/function/basic.carbon b/toolchain/semantics/testdata/function/basic.carbon
index 982a692ac806..317975b3919d 100644
--- a/toolchain/semantics/testdata/function/basic.carbon
+++ b/toolchain/semantics/testdata/function/basic.carbon
@@ -2,7 +2,7 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheckStrict} %s
+// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheck-strict} %s
 // CHECK:{
 // CHECK:  Function(
 // CHECK:      %[[ID0:[0-9]+]],
diff --git a/toolchain/semantics/testdata/function/order.carbon b/toolchain/semantics/testdata/function/order.carbon
index fc2124cbd2b4..e28cde54b917 100644
--- a/toolchain/semantics/testdata/function/order.carbon
+++ b/toolchain/semantics/testdata/function/order.carbon
@@ -2,7 +2,7 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheckStrict} %s
+// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheck-strict} %s
 // CHECK:{
 // CHECK:  Function(
 // CHECK:      %[[ID0:[0-9]+]],
diff --git a/toolchain/semantics/testdata/lit.cfg.py b/toolchain/semantics/testdata/lit.cfg.py
deleted file mode 100644
index 91efb7e33f98..000000000000
--- a/toolchain/semantics/testdata/lit.cfg.py
+++ /dev/null
@@ -1,43 +0,0 @@
-__copyright__ = """
-Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-Exceptions. See /LICENSE for license information.
-SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-"""
-
-import lit.formats
-import os
-
-
-# This is a provided variable, ignore the undefined name warning.
-config = config  # noqa: F821
-
-
-def fullpath(relative_path):
-    return os.path.join(os.environ["TEST_SRCDIR"], relative_path)
-
-
-config.name = "lit"
-config.suffixes = [".carbon"]
-config.test_format = lit.formats.ShTest()
-
-config.substitutions.append(
-    (
-        "%{carbon}",
-        fullpath("carbon/toolchain/driver/carbon"),
-    )
-)
-config.substitutions.append(("%{not}", fullpath("llvm-project/llvm/not")))
-config.substitutions.append(
-    (
-        "%{FileCheckStrict}",
-        " ".join(
-            [
-                fullpath("llvm-project/llvm/FileCheck"),
-                "--dump-input-filter=all",
-                "--implicit-check-not={{.}}",
-                "--match-full-lines",
-                "--strict-whitespace",
-            ]
-        ),
-    )
-)
diff --git a/toolchain/semantics/testdata/lit.cfg.py b/toolchain/semantics/testdata/lit.cfg.py
new file mode 120000
index 000000000000..c323f8a5e8da
--- /dev/null
+++ b/toolchain/semantics/testdata/lit.cfg.py
@@ -0,0 +1 @@
+../../../bazel/testing/lit.cfg.py
\ No newline at end of file
diff --git a/toolchain/semantics/testdata/return/binary_op.carbon b/toolchain/semantics/testdata/return/binary_op.carbon
index 624d8d5d0d44..28ed95fe67b7 100644
--- a/toolchain/semantics/testdata/return/binary_op.carbon
+++ b/toolchain/semantics/testdata/return/binary_op.carbon
@@ -2,7 +2,7 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheckStrict} %s
+// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheck-strict} %s
 // CHECK:{
 // CHECK:  Function(
 // CHECK:      %[[ID0:[0-9]+]],
diff --git a/toolchain/semantics/testdata/return/literal.carbon b/toolchain/semantics/testdata/return/literal.carbon
index e68b654a94ea..4a9690acd975 100644
--- a/toolchain/semantics/testdata/return/literal.carbon
+++ b/toolchain/semantics/testdata/return/literal.carbon
@@ -2,7 +2,7 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheckStrict} %s
+// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheck-strict} %s
 // CHECK:{
 // CHECK:  Function(
 // CHECK:      %[[ID0:[0-9]+]],
diff --git a/toolchain/semantics/testdata/return/trivial.carbon b/toolchain/semantics/testdata/return/trivial.carbon
index 222e0aa759eb..91d029477a5b 100644
--- a/toolchain/semantics/testdata/return/trivial.carbon
+++ b/toolchain/semantics/testdata/return/trivial.carbon
@@ -2,7 +2,7 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheckStrict} %s
+// RUN: %{carbon} dump semantics-ir %s 2>&1 | %{FileCheck-strict} %s
 // CHECK:{
 // CHECK:  Function(
 // CHECK:      %[[ID0:[0-9]+]],