diff --git a/explorer/file_test.cpp b/explorer/file_test.cpp
index c1ab4782ded8..7b3e5268a3d5 100644
--- a/explorer/file_test.cpp
+++ b/explorer/file_test.cpp
@@ -8,23 +8,24 @@
 namespace Carbon::Testing {
 namespace {
 
-static constexpr char PreludePath[] = "explorer/data/prelude.carbon";
-
 class ParseAndExecuteTestFile : public FileTestBase {
  public:
-  explicit ParseAndExecuteTestFile(llvm::StringRef path, bool trace)
+  explicit ParseAndExecuteTestFile(const std::filesystem::path& path,
+                                   bool trace)
       : FileTestBase(path), trace_(trace) {}
 
   auto SetUp() -> void override {
     if (trace_) {
-      if (path().find("/limits/") != llvm::StringRef::npos) {
+      std::string path_str = path().string();
+      llvm::StringRef path_ref = path_str;
+      if (path_ref.find("/limits/") != llvm::StringRef::npos) {
         GTEST_SKIP()
             << "`limits` tests check for various limit conditions (such as an "
                "infinite loop). The tests collectively don't test tracing "
                "because it creates substantial additional overhead.";
-      } else if (path().endswith(
+      } else if (path_ref.endswith(
                      "testdata/assoc_const/rewrite_large_type.carbon") ||
-                 path().endswith(
+                 path_ref.endswith(
                      "testdata/linked_list/typed_linked_list.carbon")) {
         GTEST_SKIP() << "Expensive test to trace";
       }
@@ -41,10 +42,16 @@ class ParseAndExecuteTestFile : public FileTestBase {
       trace_stream.set_stream(&trace_stream_ostream);
     }
 
+    // Set the location of the prelude.
+    char* test_srcdir = getenv("TEST_SRCDIR");
+    CARBON_CHECK(test_srcdir != nullptr);
+    std::string prelude_path(test_srcdir);
+    prelude_path += "/carbon/explorer/data/prelude.carbon";
+
     // Run the parse. Parser debug output is always off because it's difficult
     // to redirect.
     auto result =
-        ParseAndExecuteFile(PreludePath, path().str(),
+        ParseAndExecuteFile(prelude_path, path().filename().string(),
                             /*parser_debug=*/false, &trace_stream, &stdout);
     // This mirrors printing currently done by main.cpp.
     if (result.ok()) {
@@ -67,14 +74,15 @@ class ParseAndExecuteTestFile : public FileTestBase {
 
 }  // namespace
 
-extern auto RegisterFileTests(const std::vector<llvm::StringRef>& paths)
+extern auto RegisterFileTests(const std::vector<std::filesystem::path>& paths)
     -> void {
   ParseAndExecuteTestFile::RegisterTests(
-      "ParseAndExecuteTestFile", paths, [=](llvm::StringRef path) {
+      "ParseAndExecuteTestFile", paths, [=](const std::filesystem::path& path) {
         return new ParseAndExecuteTestFile(path, /*trace=*/false);
       });
   ParseAndExecuteTestFile::RegisterTests(
-      "ParseAndExecuteTestFile.trace", paths, [=](llvm::StringRef path) {
+      "ParseAndExecuteTestFile.trace", paths,
+      [=](const std::filesystem::path& path) {
         return new ParseAndExecuteTestFile(path, /*trace=*/true);
       });
 }
diff --git a/explorer/testdata/addr/fail_method_let.carbon b/explorer/testdata/addr/fail_method_let.carbon
index 57a54f5f0ebf..da0571ee4f1f 100644
--- a/explorer/testdata/addr/fail_method_let.carbon
+++ b/explorer/testdata/addr/fail_method_let.carbon
@@ -24,7 +24,7 @@ class Point {
 
 fn Main() -> i32 {
   let p: Point = Point.Origin();
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/addr/fail_method_let.carbon:[[@LINE+1]]: method p.GetSetX requires its receiver to be a reference expression
+  // CHECK:STDERR: COMPILATION ERROR: fail_method_let.carbon:[[@LINE+1]]: method p.GetSetX requires its receiver to be a reference expression
   var x: auto = p.GetSetX(42);
   if (p.x == 42) {
     return x;
diff --git a/explorer/testdata/addr/fail_method_self_misspelled.carbon b/explorer/testdata/addr/fail_method_self_misspelled.carbon
index bbc6a71c6fd4..e4bf81001297 100644
--- a/explorer/testdata/addr/fail_method_self_misspelled.carbon
+++ b/explorer/testdata/addr/fail_method_self_misspelled.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 class C {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/addr/fail_method_self_misspelled.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
+  // CHECK:STDERR: SYNTAX ERROR: fail_method_self_misspelled.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
   fn F[addr slef: Self*]() {}
 }
 
diff --git a/explorer/testdata/addr/fail_method_self_type.carbon b/explorer/testdata/addr/fail_method_self_type.carbon
index b88ac864d780..865454c96d55 100644
--- a/explorer/testdata/addr/fail_method_self_type.carbon
+++ b/explorer/testdata/addr/fail_method_self_type.carbon
@@ -28,7 +28,7 @@ class Point {
 
 fn Main() -> i32 {
   var p: Point = Point.Origin();
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/addr/fail_method_self_type.carbon:[[@LINE+3]]: type error in method access, receiver type
+  // CHECK:STDERR: COMPILATION ERROR: fail_method_self_type.carbon:[[@LINE+3]]: type error in method access, receiver type
   // CHECK:STDERR: expected: class Shape
   // CHECK:STDERR: actual: class Point
   var x: auto = p.GetSetX(42);
diff --git a/explorer/testdata/alias/fail_alias_expression.carbon b/explorer/testdata/alias/fail_alias_expression.carbon
index d9a1ad9dd4f0..4979b8351316 100644
--- a/explorer/testdata/alias/fail_alias_expression.carbon
+++ b/explorer/testdata/alias/fail_alias_expression.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/alias/fail_alias_expression.carbon:[[@LINE+1]]: invalid target for alias declaration
+// CHECK:STDERR: COMPILATION ERROR: 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 051fd10575e7..e8df86b1f52b 100644
--- a/explorer/testdata/alias/fail_alias_var.carbon
+++ b/explorer/testdata/alias/fail_alias_var.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 var v: i32;
 // TODO: This should probably be valid if we allow global variables at all.
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/alias/fail_alias_var.carbon:[[@LINE+1]]: invalid target for alias declaration
+// CHECK:STDERR: COMPILATION ERROR: 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_interface_method_as_class_member.carbon b/explorer/testdata/alias/fail_interface_method_as_class_member.carbon
index 648140477b04..44798db9b8f3 100644
--- a/explorer/testdata/alias/fail_interface_method_as_class_member.carbon
+++ b/explorer/testdata/alias/fail_interface_method_as_class_member.carbon
@@ -33,7 +33,7 @@ impl forall [U:! Printable] Vector(U) as Printable {
 
 fn Main() -> i32 {
   var v: Vector(String) = {.x = "test"};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/alias/fail_interface_method_as_class_member.carbon:[[@LINE+1]]: Member access to aliases is not yet supported.
+  // CHECK:STDERR: COMPILATION ERROR: fail_interface_method_as_class_member.carbon:[[@LINE+1]]: Member access to aliases is not yet supported.
   v.PrintIt();
   return 42;
 }
diff --git a/explorer/testdata/alias/fail_namespace_alias_member.carbon b/explorer/testdata/alias/fail_namespace_alias_member.carbon
index a4f37466c91a..88eaa753c2e5 100644
--- a/explorer/testdata/alias/fail_namespace_alias_member.carbon
+++ b/explorer/testdata/alias/fail_namespace_alias_member.carbon
@@ -10,7 +10,7 @@ namespace N;
 alias M = N;
 // TODO: It's unclear whether this should be permitted. If not, we should
 // produce a better diagnostic.
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/alias/fail_namespace_alias_member.carbon:[[@LINE+1]]: alias M cannot be used as a name qualifier
+// CHECK:STDERR: COMPILATION ERROR: fail_namespace_alias_member.carbon:[[@LINE+1]]: alias M cannot be used as a name qualifier
 fn M.F() {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/alias/fail_self_alias.carbon b/explorer/testdata/alias/fail_self_alias.carbon
index 582b202de0da..b96e08fc0cc0 100644
--- a/explorer/testdata/alias/fail_self_alias.carbon
+++ b/explorer/testdata/alias/fail_self_alias.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/alias/fail_self_alias.carbon:[[@LINE+1]]: 'a' is not usable until after it has been completely declared
+// CHECK:STDERR: COMPILATION ERROR: 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/fail_wrong_fn_alias_use.carbon b/explorer/testdata/alias/fail_wrong_fn_alias_use.carbon
index c8d98065f776..914675479276 100644
--- a/explorer/testdata/alias/fail_wrong_fn_alias_use.carbon
+++ b/explorer/testdata/alias/fail_wrong_fn_alias_use.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn F() {}
 alias A = F;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/alias/fail_wrong_fn_alias_use.carbon:[[@LINE+1]]: alias A cannot be used as a name qualifier
+// CHECK:STDERR: COMPILATION ERROR: fail_wrong_fn_alias_use.carbon:[[@LINE+1]]: alias A cannot be used as a name qualifier
 fn A.Foo() {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/alias/fail_wrong_fn_alias_use_expr.carbon b/explorer/testdata/alias/fail_wrong_fn_alias_use_expr.carbon
index 9e7cc178f311..d07362b440ac 100644
--- a/explorer/testdata/alias/fail_wrong_fn_alias_use_expr.carbon
+++ b/explorer/testdata/alias/fail_wrong_fn_alias_use_expr.carbon
@@ -10,6 +10,6 @@ fn F() {}
 alias A = F;
 
 fn Main() -> i32 {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/alias/fail_wrong_fn_alias_use_expr.carbon:[[@LINE+1]]: member access, unexpected fn () -> () in A.x
+    // CHECK:STDERR: COMPILATION ERROR: fail_wrong_fn_alias_use_expr.carbon:[[@LINE+1]]: member access, unexpected fn () -> () in A.x
     return A.x;
 }
diff --git a/explorer/testdata/alias/fail_wrong_interface_alias_use.carbon b/explorer/testdata/alias/fail_wrong_interface_alias_use.carbon
index 9eac3492aac2..b1837e0ca8de 100644
--- a/explorer/testdata/alias/fail_wrong_interface_alias_use.carbon
+++ b/explorer/testdata/alias/fail_wrong_interface_alias_use.carbon
@@ -10,6 +10,6 @@ interface Foo {}
 alias A = Foo;
 
 fn Main() -> i32 {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/alias/fail_wrong_interface_alias_use.carbon:[[@LINE+1]]: member access, bar not in interface Foo
+    // CHECK:STDERR: COMPILATION ERROR: fail_wrong_interface_alias_use.carbon:[[@LINE+1]]: member access, bar not in interface Foo
     return A.bar;
 }
diff --git a/explorer/testdata/alias/fail_wrong_namepsace_alias_use.carbon b/explorer/testdata/alias/fail_wrong_namepsace_alias_use.carbon
index 73198c09b7d1..f328c4de1812 100644
--- a/explorer/testdata/alias/fail_wrong_namepsace_alias_use.carbon
+++ b/explorer/testdata/alias/fail_wrong_namepsace_alias_use.carbon
@@ -10,6 +10,6 @@ namespace Foo;
 alias A = Foo;
 
 fn Main() -> i32 {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/alias/fail_wrong_namepsace_alias_use.carbon:[[@LINE+1]]: expected `.member_name` after name of namespace Foo
+    // CHECK:STDERR: COMPILATION ERROR: fail_wrong_namepsace_alias_use.carbon:[[@LINE+1]]: expected `.member_name` after name of namespace Foo
     return A;
 }
diff --git a/explorer/testdata/array/fail_index.carbon b/explorer/testdata/array/fail_index.carbon
index fb6a0ac7ab69..1db423532beb 100644
--- a/explorer/testdata/array/fail_index.carbon
+++ b/explorer/testdata/array/fail_index.carbon
@@ -8,6 +8,6 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: [i32; 2] = (0, 1);
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/array/fail_index.carbon:[[@LINE+1]]: index 2 out of range in (0, 1)
+  // CHECK:STDERR: RUNTIME ERROR: 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 b473a0d03559..314e772510c1 100644
--- a/explorer/testdata/array/fail_negative_size.carbon
+++ b/explorer/testdata/array/fail_negative_size.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/array/fail_negative_size.carbon:[[@LINE+1]]: Array size cannot be negative
+  // CHECK:STDERR: COMPILATION ERROR: 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_print_uninitalized_array_element.carbon b/explorer/testdata/array/fail_print_uninitalized_array_element.carbon
index 009d387252c7..1150cf488196 100644
--- a/explorer/testdata/array/fail_print_uninitalized_array_element.carbon
+++ b/explorer/testdata/array/fail_print_uninitalized_array_element.carbon
@@ -8,7 +8,7 @@ package ExplorerTest impl;
 
 fn Main() -> i32 {
   var my_array : [i32; 1];
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/array/fail_print_uninitalized_array_element.carbon:[[@LINE+1]]: Printing uninitialized value
+  // CHECK:STDERR: RUNTIME ERROR: fail_print_uninitalized_array_element.carbon:[[@LINE+1]]: Printing uninitialized value
   Print("{0}", my_array[0]);
   return 0;
 }
diff --git a/explorer/testdata/array/fail_size_mismatch.carbon b/explorer/testdata/array/fail_size_mismatch.carbon
index 047c42d92c8e..12f90d6a4d92 100644
--- a/explorer/testdata/array/fail_size_mismatch.carbon
+++ b/explorer/testdata/array/fail_size_mismatch.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/array/fail_size_mismatch.carbon:[[@LINE+1]]: type error in initializer of variable: '(i32, i32, i32)' is not implicitly convertible to '[i32; 2]'
+  // CHECK:STDERR: COMPILATION ERROR: fail_size_mismatch.carbon:[[@LINE+1]]: type error in initializer of variable: '(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/as/fail_destination_not_type.carbon b/explorer/testdata/as/fail_destination_not_type.carbon
index 24206abb498e..383a6f1896a7 100644
--- a/explorer/testdata/as/fail_destination_not_type.carbon
+++ b/explorer/testdata/as/fail_destination_not_type.carbon
@@ -7,6 +7,6 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/as/fail_destination_not_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
+  // CHECK:STDERR: COMPILATION ERROR: fail_destination_not_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
   return 4 as 7;
 }
diff --git a/explorer/testdata/as/fail_intrinsic_convert_no_args.carbon b/explorer/testdata/as/fail_intrinsic_convert_no_args.carbon
index 063e8d99de2e..f38755de8191 100644
--- a/explorer/testdata/as/fail_intrinsic_convert_no_args.carbon
+++ b/explorer/testdata/as/fail_intrinsic_convert_no_args.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/as/fail_intrinsic_convert_no_args.carbon:[[@LINE+1]]: __intrinsic_implicit_as_convert takes 2 arguments
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_convert_no_args.carbon:[[@LINE+1]]: __intrinsic_implicit_as_convert takes 2 arguments
   __intrinsic_implicit_as_convert();
   return 0;
 }
diff --git a/explorer/testdata/as/fail_intrinsic_convert_non_type.carbon b/explorer/testdata/as/fail_intrinsic_convert_non_type.carbon
index c5326db7b896..2bbad1757dcc 100644
--- a/explorer/testdata/as/fail_intrinsic_convert_non_type.carbon
+++ b/explorer/testdata/as/fail_intrinsic_convert_non_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/as/fail_intrinsic_convert_non_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_convert_non_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
   __intrinsic_implicit_as_convert("example", 0);
   return 0;
 }
diff --git a/explorer/testdata/as/fail_intrinsic_no_args.carbon b/explorer/testdata/as/fail_intrinsic_no_args.carbon
index 9915a1c973a4..e0df4f6b4377 100644
--- a/explorer/testdata/as/fail_intrinsic_no_args.carbon
+++ b/explorer/testdata/as/fail_intrinsic_no_args.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/as/fail_intrinsic_no_args.carbon:[[@LINE+1]]: __intrinsic_implicit_as takes 1 argument
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_no_args.carbon:[[@LINE+1]]: __intrinsic_implicit_as takes 1 argument
   __intrinsic_implicit_as();
   return 0;
 }
diff --git a/explorer/testdata/as/fail_intrinsic_non_type.carbon b/explorer/testdata/as/fail_intrinsic_non_type.carbon
index c2dee671b2a5..23d19fa0a135 100644
--- a/explorer/testdata/as/fail_intrinsic_non_type.carbon
+++ b/explorer/testdata/as/fail_intrinsic_non_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/as/fail_intrinsic_non_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_non_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
   __intrinsic_implicit_as(0);
   return 0;
 }
diff --git a/explorer/testdata/as/fail_no_conversion.carbon b/explorer/testdata/as/fail_no_conversion.carbon
index 70c5b22312ea..003f652586a2 100644
--- a/explorer/testdata/as/fail_no_conversion.carbon
+++ b/explorer/testdata/as/fail_no_conversion.carbon
@@ -10,7 +10,7 @@ class A { var n: i32; }
 
 fn Main() -> i32 {
   var a: A = {.n = 5};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/as/fail_no_conversion.carbon:[[@LINE+2]]: type error in `as`: `class A` is not explicitly convertible to `i32`:
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_conversion.carbon:[[@LINE+2]]: type error in `as`: `class A` is not explicitly convertible to `i32`:
   // CHECK:STDERR: could not find implementation of interface As(T = i32) for class A
   return a as i32;
 }
diff --git a/explorer/testdata/assert/fail_assert.carbon b/explorer/testdata/assert/fail_assert.carbon
index afcf17bafec4..adee17e917ba 100644
--- a/explorer/testdata/assert/fail_assert.carbon
+++ b/explorer/testdata/assert/fail_assert.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: "HALLO WELT"
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: "HALLO WELT"
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assert/fail_convert.carbon b/explorer/testdata/assert/fail_convert.carbon
index a6a42a32e42a..548b1742e8c6 100644
--- a/explorer/testdata/assert/fail_convert.carbon
+++ b/explorer/testdata/assert/fail_convert.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: "Fail"
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: "Fail"
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/assert/fail_intrinsic_bool_type.carbon b/explorer/testdata/assert/fail_intrinsic_bool_type.carbon
index d68d049f5203..dfcc36ffc7e6 100644
--- a/explorer/testdata/assert/fail_intrinsic_bool_type.carbon
+++ b/explorer/testdata/assert/fail_intrinsic_bool_type.carbon
@@ -14,7 +14,7 @@ class ConvertTo(T:! type) {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/assert/fail_intrinsic_bool_type.carbon:[[@LINE+1]]: syntax error, unexpected COMMA
+  // CHECK:STDERR: SYNTAX ERROR: fail_intrinsic_bool_type.carbon:[[@LINE+1]]: syntax error, unexpected COMMA
   __intrinsic_assert(, "unused");
   return 0;
 }
diff --git a/explorer/testdata/assert/fail_intrinsic_no_args.carbon b/explorer/testdata/assert/fail_intrinsic_no_args.carbon
index 21723f21e6f7..a6137a075aaf 100644
--- a/explorer/testdata/assert/fail_intrinsic_no_args.carbon
+++ b/explorer/testdata/assert/fail_intrinsic_no_args.carbon
@@ -14,7 +14,7 @@ class ConvertTo(T:! type) {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assert/fail_intrinsic_no_args.carbon:[[@LINE+1]]: __intrinsic_assert takes 2 arguments
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_no_args.carbon:[[@LINE+1]]: __intrinsic_assert takes 2 arguments
   __intrinsic_assert();
   return 0;
 }
diff --git a/explorer/testdata/assert/fail_intrinsic_no_convert.carbon b/explorer/testdata/assert/fail_intrinsic_no_convert.carbon
index 7a4cb87744d6..31085af553fd 100644
--- a/explorer/testdata/assert/fail_intrinsic_no_convert.carbon
+++ b/explorer/testdata/assert/fail_intrinsic_no_convert.carbon
@@ -14,7 +14,7 @@ class ConvertTo(T:! type) {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assert/fail_intrinsic_no_convert.carbon:[[@LINE+3]]: type error in __intrinsic_assert argument 0
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_no_convert.carbon:[[@LINE+3]]: type error in __intrinsic_assert argument 0
   // CHECK:STDERR: expected: bool
   // CHECK:STDERR: actual: class ConvertTo(T = bool)
   __intrinsic_assert({.v = true} as ConvertTo(bool), {.v = "Pass"} as ConvertTo(String));
diff --git a/explorer/testdata/assert/fail_intrinsic_str_type.carbon b/explorer/testdata/assert/fail_intrinsic_str_type.carbon
index c7fe88f1e878..3c2a025e5680 100644
--- a/explorer/testdata/assert/fail_intrinsic_str_type.carbon
+++ b/explorer/testdata/assert/fail_intrinsic_str_type.carbon
@@ -14,7 +14,7 @@ class ConvertTo(T:! type) {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assert/fail_intrinsic_str_type.carbon:[[@LINE+3]]: type error in __intrinsic_assert argument 1
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_str_type.carbon:[[@LINE+3]]: type error in __intrinsic_assert argument 1
   // CHECK:STDERR: expected: String
   // CHECK:STDERR: actual: i32
   __intrinsic_assert(true, 1);
diff --git a/explorer/testdata/assoc_const/fail_anonymous.carbon b/explorer/testdata/assoc_const/fail_anonymous.carbon
index 4ec48e234459..f18d6e32194d 100644
--- a/explorer/testdata/assoc_const/fail_anonymous.carbon
+++ b/explorer/testdata/assoc_const/fail_anonymous.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 interface Iface {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/assoc_const/fail_anonymous.carbon:[[@LINE+1]]: syntax error, unexpected UNDERSCORE, expecting identifier or TEMPLATE
+  // CHECK:STDERR: SYNTAX ERROR: fail_anonymous.carbon:[[@LINE+1]]: syntax error, unexpected UNDERSCORE, expecting identifier or TEMPLATE
   let _:! type;
 }
 
diff --git a/explorer/testdata/assoc_const/fail_different_type.carbon b/explorer/testdata/assoc_const/fail_different_type.carbon
index bcc23090863e..631b443d3c05 100644
--- a/explorer/testdata/assoc_const/fail_different_type.carbon
+++ b/explorer/testdata/assoc_const/fail_different_type.carbon
@@ -19,7 +19,7 @@ external impl Bad as Iface where .T = Bad {}
 
 fn Main() -> i32 {
   F(Good);
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_different_type.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.T) (with value class Bad) == i32, which is not known to be true
+  // CHECK:STDERR: COMPILATION ERROR: fail_different_type.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.T) (with value class Bad) == i32, which is not known to be true
   F(Bad);
   return 0;
 }
diff --git a/explorer/testdata/assoc_const/fail_different_value.carbon b/explorer/testdata/assoc_const/fail_different_value.carbon
index 17b7cffa47b5..7474596f9808 100644
--- a/explorer/testdata/assoc_const/fail_different_value.carbon
+++ b/explorer/testdata/assoc_const/fail_different_value.carbon
@@ -19,7 +19,7 @@ external impl Bad as Iface where .N = 4 {}
 
 fn Main() -> i32 {
   F(Good);
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_different_value.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.N) (with value 4) == 5, which is not known to be true
+  // CHECK:STDERR: COMPILATION ERROR: fail_different_value.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.N) (with value 4) == 5, which is not known to be true
   F(Bad);
   return 0;
 }
diff --git a/explorer/testdata/assoc_const/fail_equal_indirectly.carbon b/explorer/testdata/assoc_const/fail_equal_indirectly.carbon
index 1896f74e8e4a..641f34bb8e5a 100644
--- a/explorer/testdata/assoc_const/fail_equal_indirectly.carbon
+++ b/explorer/testdata/assoc_const/fail_equal_indirectly.carbon
@@ -24,7 +24,7 @@ fn G[U:! type where .Self == i32, T:! Iface where .T = U](x: T, y: U) {
 
 // Not OK: would require looking through two levels of `==`.
 fn H[V:! type where .Self == i32, W:! Iface where .T == V](x: W, y: V) {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_equal_indirectly.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.T) (with value (W).(Iface.T)) == i32, which is not known to be true
+  // CHECK:STDERR: COMPILATION ERROR: fail_equal_indirectly.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.T) (with value (W).(Iface.T)) == i32, which is not known to be true
   F(x);
 }
 
diff --git a/explorer/testdata/assoc_const/fail_equal_to_dependent_type.carbon b/explorer/testdata/assoc_const/fail_equal_to_dependent_type.carbon
index 4503867ece72..adfc001ef1a5 100644
--- a/explorer/testdata/assoc_const/fail_equal_to_dependent_type.carbon
+++ b/explorer/testdata/assoc_const/fail_equal_to_dependent_type.carbon
@@ -17,7 +17,7 @@ fn G[U:! Iface where .T == i32](x: U) {
 }
 
 fn H[V:! Iface](x: V) {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_equal_to_dependent_type.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.T) (with value (V).(Iface.T)) == i32, which is not known to be true
+  // CHECK:STDERR: COMPILATION ERROR: fail_equal_to_dependent_type.carbon:[[@LINE+1]]: constraint requires that (T).(Iface.T) (with value (V).(Iface.T)) == i32, which is not known to be true
   F(x);
 }
 
diff --git a/explorer/testdata/assoc_const/fail_implied_constraints.carbon b/explorer/testdata/assoc_const/fail_implied_constraints.carbon
index 031badfcdc5f..5bec7498902c 100644
--- a/explorer/testdata/assoc_const/fail_implied_constraints.carbon
+++ b/explorer/testdata/assoc_const/fail_implied_constraints.carbon
@@ -16,7 +16,7 @@ interface Z {
   // We reject this even though it is the responsibility of the `impl as Z` to
   // provide a type `N` such that `i32 is X(N)`. We might want to treat this as
   // an implied constraint and allow this in the future.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_implied_constraints.carbon:[[@LINE+1]]: could not find implementation of interface X(T = N) for i32
+  // CHECK:STDERR: COMPILATION ERROR: fail_implied_constraints.carbon:[[@LINE+1]]: could not find implementation of interface X(T = N) for i32
   let N:! Y(.Self) where .M = i32;
 }
 
diff --git a/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon b/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon
index 9928b2546fde..ee0df8a3d57a 100644
--- a/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon
+++ b/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon
@@ -12,7 +12,7 @@ interface HasThreeTypes {
   let C:! type;
 }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon:[[@LINE+1]]: implementation doesn't provide a concrete value for interface HasThreeTypes.B
+// CHECK:STDERR: COMPILATION ERROR: fail_incomplete_impl_1.carbon:[[@LINE+1]]: implementation doesn't provide a concrete value for interface 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 adb1780439a7..8b706d4874c1 100644
--- a/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon
+++ b/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon
@@ -12,7 +12,7 @@ interface HasThreeTypes {
   let C:! type;
 }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon:[[@LINE+1]]: implementation doesn't provide a concrete value for interface HasThreeTypes.C
+// CHECK:STDERR: COMPILATION ERROR: fail_incomplete_impl_2.carbon:[[@LINE+1]]: implementation doesn't provide a concrete value for interface HasThreeTypes.C
 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 1f44b33edd4f..03db84b0f18b 100644
--- a/explorer/testdata/assoc_const/fail_indirectly_equal.carbon
+++ b/explorer/testdata/assoc_const/fail_indirectly_equal.carbon
@@ -21,7 +21,7 @@ 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:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_indirectly_equal.carbon:[[@LINE+1]]: type error in return value: '(T).(A.T)' is not implicitly convertible to '(U).(A.T)'
+  // CHECK:STDERR: COMPILATION ERROR: fail_indirectly_equal.carbon:[[@LINE+1]]: type error in return value: '(T).(A.T)' is not implicitly convertible to '(U).(A.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 6a5b04a1bdb5..5d8262dd97df 100644
--- a/explorer/testdata/assoc_const/fail_match_in_deduction.carbon
+++ b/explorer/testdata/assoc_const/fail_match_in_deduction.carbon
@@ -20,7 +20,7 @@ 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:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_match_in_deduction.carbon:[[@LINE+1]]: mismatch in non-deduced values, `(V).(Vector.Dim)` != `3`
+  // CHECK:STDERR: COMPILATION ERROR: fail_match_in_deduction.carbon:[[@LINE+1]]: mismatch in non-deduced values, `(V).(Vector.Dim)` != `3`
   G(p);
 }
 
diff --git a/explorer/testdata/assoc_const/fail_missing_equal.carbon b/explorer/testdata/assoc_const/fail_missing_equal.carbon
index 7bba99dd9e7e..dea62d9af895 100644
--- a/explorer/testdata/assoc_const/fail_missing_equal.carbon
+++ b/explorer/testdata/assoc_const/fail_missing_equal.carbon
@@ -16,7 +16,7 @@ fn A[T:! Container where .Element == i32](x: T) -> T.Element {
 }
 
 fn B[T:! Container](x: T) -> T.Element {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_missing_equal.carbon:[[@LINE+1]]: constraint requires that (T).(Container.Element) (with value (T).(Container.Element)) == i32, which is not known to be true
+  // CHECK:STDERR: COMPILATION ERROR: fail_missing_equal.carbon:[[@LINE+1]]: constraint requires that (T).(Container.Element) (with value (T).(Container.Element)) == i32, which is not known to be true
   return A(x);
 }
 
diff --git a/explorer/testdata/assoc_const/fail_missing_rewrite.carbon b/explorer/testdata/assoc_const/fail_missing_rewrite.carbon
index 3ee47c41edda..b9f2a8f7a34c 100644
--- a/explorer/testdata/assoc_const/fail_missing_rewrite.carbon
+++ b/explorer/testdata/assoc_const/fail_missing_rewrite.carbon
@@ -16,7 +16,7 @@ fn A[T:! Container where .Element = i32](x: T) -> T.Element {
 }
 
 fn B[T:! Container](x: T) -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_missing_rewrite.carbon:[[@LINE+1]]: constraint requires that (T).(Container.Element) (with value (T).(Container.Element)) == i32, which is not known to be true
+  // CHECK:STDERR: COMPILATION ERROR: fail_missing_rewrite.carbon:[[@LINE+1]]: constraint requires that (T).(Container.Element) (with value (T).(Container.Element)) == i32, which is not known to be true
   return A(x);
 }
 
diff --git a/explorer/testdata/assoc_const/fail_multiple_deduction.carbon b/explorer/testdata/assoc_const/fail_multiple_deduction.carbon
index 5fc7f1d22f77..8562afb2a7fa 100644
--- a/explorer/testdata/assoc_const/fail_multiple_deduction.carbon
+++ b/explorer/testdata/assoc_const/fail_multiple_deduction.carbon
@@ -14,7 +14,7 @@ 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:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_multiple_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! type:
+  // CHECK:STDERR: COMPILATION ERROR: fail_multiple_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! type:
   // CHECK:STDERR:   (X).(HasThreeTypes.A)
   // CHECK:STDERR:   (X).(HasThreeTypes.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 1454118927fc..50593515bf53 100644
--- a/explorer/testdata/assoc_const/fail_overspecified_impl.carbon
+++ b/explorer/testdata/assoc_const/fail_overspecified_impl.carbon
@@ -10,7 +10,7 @@ interface HasType {
   let T:! type;
 }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_overspecified_impl.carbon:[[@LINE+3]]: multiple different rewrites for `(i32).(HasType.T)`:
+// CHECK:STDERR: COMPILATION ERROR: fail_overspecified_impl.carbon:[[@LINE+3]]: multiple different rewrites for `(i32).(HasType.T)`:
 // CHECK:STDERR:   i32
 // CHECK:STDERR:   {.a: i32}
 external impl i32 as HasType where .T = i32 and .T = {.a: i32} {}
diff --git a/explorer/testdata/assoc_const/fail_redefined.carbon b/explorer/testdata/assoc_const/fail_redefined.carbon
index 2d9941febd55..41d565fab3a6 100644
--- a/explorer/testdata/assoc_const/fail_redefined.carbon
+++ b/explorer/testdata/assoc_const/fail_redefined.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 interface Iface {
   let T:! type;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_redefined.carbon:[[@LINE+1]]: Duplicate name `T` also found at explorer/testdata/assoc_const/fail_redefined.carbon:[[@LINE-1]]
+  // CHECK:STDERR: COMPILATION ERROR: fail_redefined.carbon:[[@LINE+1]]: Duplicate name `T` also found at fail_redefined.carbon:[[@LINE-1]]
   let T:! type;
 }
 
diff --git a/explorer/testdata/assoc_const/fail_rewrite_creates_infinite_type.carbon b/explorer/testdata/assoc_const/fail_rewrite_creates_infinite_type.carbon
index 87794f49dc92..ad504f2fa615 100644
--- a/explorer/testdata/assoc_const/fail_rewrite_creates_infinite_type.carbon
+++ b/explorer/testdata/assoc_const/fail_rewrite_creates_infinite_type.carbon
@@ -10,7 +10,7 @@ interface HasType {
   let T:! type;
 }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_rewrite_creates_infinite_type.carbon:[[@LINE+1]]: rewrite of (H).(HasType.T) applies within its own resolved expansion of (H).(HasType.T)*
+// CHECK:STDERR: COMPILATION ERROR: fail_rewrite_creates_infinite_type.carbon:[[@LINE+1]]: rewrite of (H).(HasType.T) applies within its own resolved expansion of (H).(HasType.T)*
 fn F[H:! HasType where .T = .T*]() {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/assoc_const/fail_rewrite_cycle.carbon b/explorer/testdata/assoc_const/fail_rewrite_cycle.carbon
index 500933f67a50..35cc00b22348 100644
--- a/explorer/testdata/assoc_const/fail_rewrite_cycle.carbon
+++ b/explorer/testdata/assoc_const/fail_rewrite_cycle.carbon
@@ -30,7 +30,7 @@ fn F[
     .T6 = .T7 and
     .T7 = .T8 and
     .T8 = .T9 and
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_rewrite_cycle.carbon:[[@LINE+1]]: rewrite of (M).(ManyTypes.T4) applies within its own resolved expansion of (M).(ManyTypes.T4)
+    // CHECK:STDERR: COMPILATION ERROR: fail_rewrite_cycle.carbon:[[@LINE+1]]: rewrite of (M).(ManyTypes.T4) applies within its own resolved expansion of (M).(ManyTypes.T4)
     .T9 = .T0]() {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/assoc_const/fail_rewrite_depends_on_later_rewrite.carbon b/explorer/testdata/assoc_const/fail_rewrite_depends_on_later_rewrite.carbon
index 6df685ed5daf..c79bf7dbd5ce 100644
--- a/explorer/testdata/assoc_const/fail_rewrite_depends_on_later_rewrite.carbon
+++ b/explorer/testdata/assoc_const/fail_rewrite_depends_on_later_rewrite.carbon
@@ -11,7 +11,7 @@ interface HasTypeAndValue {
   let V:! T;
 }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_rewrite_depends_on_later_rewrite.carbon:[[@LINE+1]]: type error in rewrite constraint: 'i32' is not implicitly convertible to '(X).(HasTypeAndValue.T)'
+// CHECK:STDERR: COMPILATION ERROR: fail_rewrite_depends_on_later_rewrite.carbon:[[@LINE+1]]: type error in rewrite constraint: 'i32' is not implicitly convertible to '(X).(HasTypeAndValue.T)'
 fn F(X:! HasTypeAndValue where .V = 5 and .T = i32) -> i32 { return X.V; }
 
 impl i32 as HasTypeAndValue where .T = i32 and .V = 5 {}
diff --git a/explorer/testdata/assoc_const/fail_simple_rewrite_cycle_1.carbon b/explorer/testdata/assoc_const/fail_simple_rewrite_cycle_1.carbon
index 26507cd27075..294069085bbe 100644
--- a/explorer/testdata/assoc_const/fail_simple_rewrite_cycle_1.carbon
+++ b/explorer/testdata/assoc_const/fail_simple_rewrite_cycle_1.carbon
@@ -13,7 +13,7 @@ interface TwoTypes {
 
 // Attempting to fully resolve the replacement for `.T` would never create a
 // situation where `.T`'s expansion involves `.T`. Ensure we catch this anyway.
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_simple_rewrite_cycle_1.carbon:[[@LINE+1]]: rewrite of (X).(TwoTypes.U) applies within its own resolved expansion of (X).(TwoTypes.U)*
+// CHECK:STDERR: COMPILATION ERROR: fail_simple_rewrite_cycle_1.carbon:[[@LINE+1]]: rewrite of (X).(TwoTypes.U) applies within its own resolved expansion of (X).(TwoTypes.U)*
 fn F[X:! TwoTypes where .T = .U and .U = .U*]() {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/assoc_const/fail_simple_rewrite_cycle_2.carbon b/explorer/testdata/assoc_const/fail_simple_rewrite_cycle_2.carbon
index c718b2f7a56a..92e86118686d 100644
--- a/explorer/testdata/assoc_const/fail_simple_rewrite_cycle_2.carbon
+++ b/explorer/testdata/assoc_const/fail_simple_rewrite_cycle_2.carbon
@@ -13,7 +13,7 @@ interface TwoTypes {
 
 // Attempting to fully resolve the replacement for `.T` would never create a
 // situation where `.T`'s expansion involves `.T`. Ensure we catch this anyway.
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_simple_rewrite_cycle_2.carbon:[[@LINE+1]]: rewrite of (X).(TwoTypes.U) applies within its own resolved expansion of (X).(TwoTypes.U)*
+// CHECK:STDERR: COMPILATION ERROR: fail_simple_rewrite_cycle_2.carbon:[[@LINE+1]]: rewrite of (X).(TwoTypes.U) applies within its own resolved expansion of (X).(TwoTypes.U)*
 fn F[X:! TwoTypes where .U = .U* and .T = .U]() {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/assoc_const/fail_unknown_value.carbon b/explorer/testdata/assoc_const/fail_unknown_value.carbon
index b30d797062a4..4f27ca31038c 100644
--- a/explorer/testdata/assoc_const/fail_unknown_value.carbon
+++ b/explorer/testdata/assoc_const/fail_unknown_value.carbon
@@ -11,7 +11,7 @@ interface Iface { let N:! i32; }
 fn PickType(N: i32) -> type { return i32; }
 
 fn F[T:! Iface](x: T) -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_unknown_value.carbon:[[@LINE+1]]: value of associated constant (T).(Iface.N) is not known
+  // CHECK:STDERR: COMPILATION ERROR: 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 1692055d6e78..725c7d1c9ca3 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
@@ -12,7 +12,7 @@ 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:STDERR: COMPILATION ERROR: explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon:[[@LINE+1]]: value of associated constant (T).(Iface.N) is not known
+  // CHECK:STDERR: COMPILATION ERROR: fail_unknown_value_specified_in_constraint.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/auto/fail_use_in_init.carbon b/explorer/testdata/auto/fail_use_in_init.carbon
index 21cd0e331219..0f0c2976f87e 100644
--- a/explorer/testdata/auto/fail_use_in_init.carbon
+++ b/explorer/testdata/auto/fail_use_in_init.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   // TODO: The error here should be that we aren't allowed to refer to 'a' yet.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/auto/fail_use_in_init.carbon:[[@LINE+1]]: could not resolve 'a'
+  // CHECK:STDERR: COMPILATION ERROR: fail_use_in_init.carbon:[[@LINE+1]]: could not resolve 'a'
   var a: auto = a;
   return 0;
 }
diff --git a/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon b/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon
index b445f5221d42..fe1ed983a76e 100644
--- a/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon
+++ b/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/basic_syntax/fail_alternative_not_type.carbon:[[@LINE+1]]: type error in type expression: '(i32,)' is not implicitly convertible to 'type'
+// CHECK:STDERR: COMPILATION ERROR: fail_alternative_not_type.carbon:[[@LINE+1]]: type error in type expression: '(i32,)' is not implicitly convertible to 'type'
 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 e95eb99e523e..c4b9fd8cf280 100644
--- a/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon
+++ b/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 choice Ch {
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 1d6829d69197..e7ab425ff00e 100644
--- a/explorer/testdata/basic_syntax/fail_assign_to_function.carbon
+++ b/explorer/testdata/basic_syntax/fail_assign_to_function.carbon
@@ -10,7 +10,7 @@ fn F() {}
 fn G() {}
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/basic_syntax/fail_assign_to_function.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `F`
+  // CHECK:STDERR: COMPILATION ERROR: fail_assign_to_function.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `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 2cc5f10b94c9..e45394e4e731 100644
--- a/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon
+++ b/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/basic_syntax/fail_assign_to_rval.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `1`
+  // CHECK:STDERR: COMPILATION ERROR: fail_assign_to_rval.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `1`
   1 = 0;
   return 0;
 }
diff --git a/explorer/testdata/basic_syntax/fail_block.carbon b/explorer/testdata/basic_syntax/fail_block.carbon
index 2099fbf6cdb1..2e0266db484d 100644
--- a/explorer/testdata/basic_syntax/fail_block.carbon
+++ b/explorer/testdata/basic_syntax/fail_block.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   {
-    // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/basic_syntax/fail_block.carbon:[[@LINE+1]]: syntax error, unexpected RETURN, expecting PERIOD or RIGHT_CURLY_BRACE
+    // CHECK:STDERR: SYNTAX ERROR: 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_extra_parens.carbon b/explorer/testdata/basic_syntax/fail_choice_extra_parens.carbon
index 5821b6a7e834..c1a25786a984 100644
--- a/explorer/testdata/basic_syntax/fail_choice_extra_parens.carbon
+++ b/explorer/testdata/basic_syntax/fail_choice_extra_parens.carbon
@@ -13,7 +13,7 @@ choice Ints {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/basic_syntax/fail_choice_extra_parens.carbon:[[@LINE+1]]: alternative `choice Ints.None` does not expect an argument list
+  // CHECK:STDERR: COMPILATION ERROR: fail_choice_extra_parens.carbon:[[@LINE+1]]: alternative `choice Ints.None` does not expect an argument list
   match (Ints.None()) {
     case Ints.None => { return 0; }
     default => { return 1; }
diff --git a/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon b/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon
index 6c41b507b726..276c852e8fca 100644
--- a/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon
+++ b/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon
@@ -15,7 +15,7 @@ choice Ints {
 fn Main() -> i32 {
   match (Ints.None) {
     case Ints.None() => { return 0; }
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/basic_syntax/fail_choice_no_parens.carbon:[[@LINE+3]]: type error in `match` pattern type
+    // CHECK:STDERR: COMPILATION ERROR: fail_choice_no_parens.carbon:[[@LINE+3]]: type error in `match` pattern type
     // CHECK:STDERR: expected: choice Ints
     // CHECK:STDERR: actual: fn () -> choice Ints
     default => { return 1; }
diff --git a/explorer/testdata/basic_syntax/fail_choice_pattern_extra_parens.carbon b/explorer/testdata/basic_syntax/fail_choice_pattern_extra_parens.carbon
index 89961699a38e..9c0d7bbe661a 100644
--- a/explorer/testdata/basic_syntax/fail_choice_pattern_extra_parens.carbon
+++ b/explorer/testdata/basic_syntax/fail_choice_pattern_extra_parens.carbon
@@ -14,7 +14,7 @@ choice Ints {
 
 fn Main() -> i32 {
   match (Ints.None) {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/basic_syntax/fail_choice_pattern_extra_parens.carbon:[[@LINE+1]]: alternative `choice Ints.None` does not expect an argument list
+    // CHECK:STDERR: COMPILATION ERROR: fail_choice_pattern_extra_parens.carbon:[[@LINE+1]]: alternative `choice Ints.None` does not expect an argument list
     case Ints.None() => { return 0; }
     default => { return 1; }
   }
diff --git a/explorer/testdata/basic_syntax/fail_choice_pattern_no_parens.carbon b/explorer/testdata/basic_syntax/fail_choice_pattern_no_parens.carbon
index 5de8807b1d42..a51011576abe 100644
--- a/explorer/testdata/basic_syntax/fail_choice_pattern_no_parens.carbon
+++ b/explorer/testdata/basic_syntax/fail_choice_pattern_no_parens.carbon
@@ -15,7 +15,7 @@ choice Ints {
 fn Main() -> i32 {
   match (Ints.None()) {
     case Ints.None => { return 0; }
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/basic_syntax/fail_choice_pattern_no_parens.carbon:[[@LINE+3]]: type error in `match` pattern type
+    // CHECK:STDERR: COMPILATION ERROR: fail_choice_pattern_no_parens.carbon:[[@LINE+3]]: type error in `match` pattern type
     // CHECK:STDERR: expected: fn () -> choice Ints
     // CHECK:STDERR: actual: choice Ints
     default => { return 1; }
diff --git a/explorer/testdata/basic_syntax/fail_compare_precedence.carbon b/explorer/testdata/basic_syntax/fail_compare_precedence.carbon
index 3d39157c63f5..285ea47d6e6c 100644
--- a/explorer/testdata/basic_syntax/fail_compare_precedence.carbon
+++ b/explorer/testdata/basic_syntax/fail_compare_precedence.carbon
@@ -7,6 +7,6 @@
 package ExplorerTest api;
 
 fn CompareBools(a: bool, b: bool) -> bool {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/basic_syntax/fail_compare_precedence.carbon:[[@LINE+1]]: syntax error, unexpected EQUAL_EQUAL, expecting SEMICOLON
+  // CHECK:STDERR: SYNTAX ERROR: fail_compare_precedence.carbon:[[@LINE+1]]: syntax error, unexpected EQUAL_EQUAL, expecting SEMICOLON
   return not a == b;
 }
diff --git a/explorer/testdata/basic_syntax/fail_invalid_char.carbon b/explorer/testdata/basic_syntax/fail_invalid_char.carbon
index 702671d2c056..c83b78705689 100644
--- a/explorer/testdata/basic_syntax/fail_invalid_char.carbon
+++ b/explorer/testdata/basic_syntax/fail_invalid_char.carbon
@@ -4,5 +4,5 @@
 //
 // AUTOUPDATE
 
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/basic_syntax/fail_invalid_char.carbon:[[@LINE+1]]: invalid character '\xEF' in source file.
+// CHECK:STDERR: SYNTAX ERROR: 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 413481d7fe72..86940b5e3a33 100644
--- a/explorer/testdata/basic_syntax/fail_invalid_integer.carbon
+++ b/explorer/testdata/basic_syntax/fail_invalid_integer.carbon
@@ -7,6 +7,6 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/basic_syntax/fail_invalid_integer.carbon:[[@LINE+1]]: Invalid integer literal: 11111111111111111111111111
+  // CHECK:STDERR: SYNTAX ERROR: 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 45959f3d0126..2c6aee5f8036 100644
--- a/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon
+++ b/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon:[[@LINE+1]]: Invalid type literal: i11111111111111111111111111
+  // CHECK:STDERR: SYNTAX ERROR: 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_unimplemented_example.carbon b/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon
index 8d06ff961126..cb952f94adc2 100644
--- a/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon
+++ b/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon
@@ -7,6 +7,6 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/basic_syntax/fail_unimplemented_example.carbon:[[@LINE+1]]: Unimplemented
+  // CHECK:STDERR: COMPILATION ERROR: 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 f5411e7cab6d..c2bb5f341916 100644
--- a/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon
+++ b/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon
@@ -7,6 +7,6 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon:[[@LINE+1]]: Unknown intrinsic 'nonexistent'
+  // CHECK:STDERR: SYNTAX ERROR: 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 b53d17a7452b..fff463f9d723 100644
--- a/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon
+++ b/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon:[[@LINE+1]]: Only i32 is supported for now: i64
+  // CHECK:STDERR: SYNTAX ERROR: 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/choice/fail_recursive_use.carbon b/explorer/testdata/choice/fail_recursive_use.carbon
index 0fc34199f04d..b80256ab8c7d 100644
--- a/explorer/testdata/choice/fail_recursive_use.carbon
+++ b/explorer/testdata/choice/fail_recursive_use.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 choice C {
   X,
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/choice/fail_recursive_use.carbon:[[@LINE+1]]: 'C' is not usable until after it has been completely declared
+  // CHECK:STDERR: COMPILATION ERROR: fail_recursive_use.carbon:[[@LINE+1]]: 'C' is not usable until after it has been completely declared
   Y(if C.X then i32 else i32)
 }
 
diff --git a/explorer/testdata/class/fail_abstract_method_not_supported.carbon b/explorer/testdata/class/fail_abstract_method_not_supported.carbon
index 70885ec0587f..824d3ef87aa9 100644
--- a/explorer/testdata/class/fail_abstract_method_not_supported.carbon
+++ b/explorer/testdata/class/fail_abstract_method_not_supported.carbon
@@ -12,7 +12,7 @@ base class C {
 class D extends C {
   abstract fn Foo[self:Self]() -> i32 {
     return 1;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_abstract_method_not_supported.carbon:[[@LINE+1]]: Error declaring `Foo`: `abstract` methods are not yet supported.
+  // CHECK:STDERR: COMPILATION ERROR: fail_abstract_method_not_supported.carbon:[[@LINE+1]]: Error declaring `Foo`: `abstract` methods are not yet supported.
   }
 }
 
diff --git a/explorer/testdata/class/fail_call_method_before_typecheck.carbon b/explorer/testdata/class/fail_call_method_before_typecheck.carbon
index 332c258ae96f..b54bc69f2a75 100644
--- a/explorer/testdata/class/fail_call_method_before_typecheck.carbon
+++ b/explorer/testdata/class/fail_call_method_before_typecheck.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 class A {
   fn F[self: Self]() -> type {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_call_method_before_typecheck.carbon:[[@LINE+1]]: attempt to call function `F` that has not been fully type-checked
+    // CHECK:STDERR: COMPILATION ERROR: fail_call_method_before_typecheck.carbon:[[@LINE+1]]: attempt to call function `F` that has not been fully type-checked
     var a: ({} as A).F() = 0;
     return i32;
   }
diff --git a/explorer/testdata/class/fail_call_undefined_method.carbon b/explorer/testdata/class/fail_call_undefined_method.carbon
index b9b1dc7efa0c..37998dabe8b9 100644
--- a/explorer/testdata/class/fail_call_undefined_method.carbon
+++ b/explorer/testdata/class/fail_call_undefined_method.carbon
@@ -12,6 +12,6 @@ class A {
 
 fn Main() -> i32 {
   var a: A = {};
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/class/fail_call_undefined_method.carbon:[[@LINE+1]]: attempt to call function `F` that has not been defined
+  // CHECK:STDERR: RUNTIME ERROR: fail_call_undefined_method.carbon:[[@LINE+1]]: attempt to call function `F` that has not been defined
   return a.F();
 }
diff --git a/explorer/testdata/class/fail_class_named_self.carbon b/explorer/testdata/class/fail_class_named_self.carbon
index 11374be25ab6..f6cdf2b263c0 100644
--- a/explorer/testdata/class/fail_class_named_self.carbon
+++ b/explorer/testdata/class/fail_class_named_self.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 // Error: Can't use keyword `Self` as the name of a class.
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/class/fail_class_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier or LEFT_PARENTHESIS
+// CHECK:STDERR: SYNTAX ERROR: fail_class_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier or LEFT_PARENTHESIS
 class Self {
   var x: i32;
   var y: i32;
diff --git a/explorer/testdata/class/fail_direct_base_class_init.carbon b/explorer/testdata/class/fail_direct_base_class_init.carbon
index 9395399545cf..67c898a77f0d 100644
--- a/explorer/testdata/class/fail_direct_base_class_init.carbon
+++ b/explorer/testdata/class/fail_direct_base_class_init.carbon
@@ -15,7 +15,7 @@ class B extends A {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_direct_base_class_init.carbon:[[@LINE+1]]: type error in initializer of variable: '{.a: i32, .b: i32}' is not implicitly convertible to 'class B'
+  // CHECK:STDERR: COMPILATION ERROR: fail_direct_base_class_init.carbon:[[@LINE+1]]: type error in initializer of variable: '{.a: i32, .b: i32}' is not implicitly convertible to 'class B'
   var b: B = {.a=0, .b=1};
   return 0;
 }
diff --git a/explorer/testdata/class/fail_extends_final_class.carbon b/explorer/testdata/class/fail_extends_final_class.carbon
index 279c10b9c8a4..9cfe488840d5 100644
--- a/explorer/testdata/class/fail_extends_final_class.carbon
+++ b/explorer/testdata/class/fail_extends_final_class.carbon
@@ -12,7 +12,7 @@ class C {
 
 class D extends C {
   fn G() {}
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_extends_final_class.carbon:[[@LINE+1]]: Base class `C` is `final` and cannot be inherited. Add the `base` or `abstract` class prefix to `C` to allow it to be inherited
+// CHECK:STDERR: COMPILATION ERROR: fail_extends_final_class.carbon:[[@LINE+1]]: Base class `C` is `final` and cannot be inherited. Add the `base` or `abstract` class prefix to `C` to allow it to be inherited
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/class/fail_extends_non_class.carbon b/explorer/testdata/class/fail_extends_non_class.carbon
index 99a7ade869d0..eb8d67ee9ce3 100644
--- a/explorer/testdata/class/fail_extends_non_class.carbon
+++ b/explorer/testdata/class/fail_extends_non_class.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_extends_non_class.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
+// CHECK:STDERR: COMPILATION ERROR: fail_extends_non_class.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
 class C extends 3 {
   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 0d356e6d1a68..ef311c738af6 100644
--- a/explorer/testdata/class/fail_field_access_mismatch.carbon
+++ b/explorer/testdata/class/fail_field_access_mismatch.carbon
@@ -13,6 +13,6 @@ class Point {
 
 fn Main() -> i32 {
   var p: Point = {.x = 1, .y = 2};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_field_access_mismatch.carbon:[[@LINE+1]]: class Point does not have a field named z
+  // CHECK:STDERR: COMPILATION ERROR: 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_access_mismatch_base.carbon b/explorer/testdata/class/fail_field_access_mismatch_base.carbon
index 179c28274d05..294395ab7f1b 100644
--- a/explorer/testdata/class/fail_field_access_mismatch_base.carbon
+++ b/explorer/testdata/class/fail_field_access_mismatch_base.carbon
@@ -17,6 +17,6 @@ class Point3D extends Point {
 
 fn Main() -> i32 {
   var p: Point3D = {.base={.x = 1, .y = 2}, .z = 3};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_field_access_mismatch_base.carbon:[[@LINE+1]]: class Point3D does not have a field named a
+  // CHECK:STDERR: COMPILATION ERROR: fail_field_access_mismatch_base.carbon:[[@LINE+1]]: class Point3D does not have a field named a
   return p.a;
 }
diff --git a/explorer/testdata/class/fail_field_assign_mismatch_base.carbon b/explorer/testdata/class/fail_field_assign_mismatch_base.carbon
index 69886f0b9e0a..40585a3c37ef 100644
--- a/explorer/testdata/class/fail_field_assign_mismatch_base.carbon
+++ b/explorer/testdata/class/fail_field_assign_mismatch_base.carbon
@@ -17,7 +17,7 @@ class Point3D extends Point {
 
 fn Main() -> i32 {
   var p: Point3D = {.base={.x = 1, .y = 2}, .z = 3};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_field_assign_mismatch_base.carbon:[[@LINE+1]]: class Point3D does not have a field named a
+  // CHECK:STDERR: COMPILATION ERROR: fail_field_assign_mismatch_base.carbon:[[@LINE+1]]: class Point3D does not have a field named a
   p.a = 0;
   return 0;
 }
diff --git a/explorer/testdata/class/fail_field_mismatch.carbon b/explorer/testdata/class/fail_field_mismatch.carbon
index 073186074772..d1ccdf71f746 100644
--- a/explorer/testdata/class/fail_field_mismatch.carbon
+++ b/explorer/testdata/class/fail_field_mismatch.carbon
@@ -12,7 +12,7 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_field_mismatch.carbon:[[@LINE+1]]: type error in initializer of variable: '{.x: i32, .z: i32}' is not implicitly convertible to 'class Point'
+  // CHECK:STDERR: COMPILATION ERROR: fail_field_mismatch.carbon:[[@LINE+1]]: type error in initializer of variable: '{.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 0438ada5f825..5ccbb74f7401 100644
--- a/explorer/testdata/class/fail_field_missing.carbon
+++ b/explorer/testdata/class/fail_field_missing.carbon
@@ -12,7 +12,7 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_field_missing.carbon:[[@LINE+1]]: type error in initializer of variable: '{.x: i32}' is not implicitly convertible to 'class Point'
+  // CHECK:STDERR: COMPILATION ERROR: fail_field_missing.carbon:[[@LINE+1]]: type error in initializer of variable: '{.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_impl_method_not_existing.carbon b/explorer/testdata/class/fail_impl_method_not_existing.carbon
index 4dce79018ec2..44612a9cf872 100644
--- a/explorer/testdata/class/fail_impl_method_not_existing.carbon
+++ b/explorer/testdata/class/fail_impl_method_not_existing.carbon
@@ -12,7 +12,7 @@ base class C {
 class D extends C {
   impl fn Foo[self:Self]() -> i32 {
     return 1;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_impl_method_not_existing.carbon:[[@LINE+1]]: Error declaring `Foo`: cannot override a method that is not declared `abstract` or `virtual` in base class.
+  // CHECK:STDERR: COMPILATION ERROR: fail_impl_method_not_existing.carbon:[[@LINE+1]]: Error declaring `Foo`: cannot override a method that is not declared `abstract` or `virtual` in base class.
   }
 }
 
diff --git a/explorer/testdata/class/fail_impl_method_not_virtual.carbon b/explorer/testdata/class/fail_impl_method_not_virtual.carbon
index 5ccc09a71ebf..0a64d878e17c 100644
--- a/explorer/testdata/class/fail_impl_method_not_virtual.carbon
+++ b/explorer/testdata/class/fail_impl_method_not_virtual.carbon
@@ -15,7 +15,7 @@ base class C {
 class D extends C {
   impl fn Foo[self:Self]() -> i32 {
     return 1;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_impl_method_not_virtual.carbon:[[@LINE+1]]: Error declaring `Foo`: cannot override a method that is not declared `abstract` or `virtual` in base class.
+  // CHECK:STDERR: COMPILATION ERROR: fail_impl_method_not_virtual.carbon:[[@LINE+1]]: Error declaring `Foo`: cannot override a method that is not declared `abstract` or `virtual` in base class.
   }
 }
 
diff --git a/explorer/testdata/class/fail_instantiate_abstract_class_constructor.carbon b/explorer/testdata/class/fail_instantiate_abstract_class_constructor.carbon
index 55e910b6d0eb..febc0294859f 100644
--- a/explorer/testdata/class/fail_instantiate_abstract_class_constructor.carbon
+++ b/explorer/testdata/class/fail_instantiate_abstract_class_constructor.carbon
@@ -15,7 +15,7 @@ abstract class C {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_instantiate_abstract_class_constructor.carbon:[[@LINE+1]]: Cannot instantiate abstract class C
+  // CHECK:STDERR: COMPILATION ERROR: fail_instantiate_abstract_class_constructor.carbon:[[@LINE+1]]: Cannot instantiate abstract class C
   var c: C = C.Create();
   return 0;
 }
diff --git a/explorer/testdata/class/fail_instantiate_abstract_class_empty.carbon b/explorer/testdata/class/fail_instantiate_abstract_class_empty.carbon
index c461ebc1556f..655cbfb3ced8 100644
--- a/explorer/testdata/class/fail_instantiate_abstract_class_empty.carbon
+++ b/explorer/testdata/class/fail_instantiate_abstract_class_empty.carbon
@@ -11,7 +11,7 @@ abstract class C {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_instantiate_abstract_class_empty.carbon:[[@LINE+1]]: Cannot instantiate abstract class C
+  // CHECK:STDERR: COMPILATION ERROR: fail_instantiate_abstract_class_empty.carbon:[[@LINE+1]]: Cannot instantiate abstract class C
   var c: C;
   return 0;
 }
diff --git a/explorer/testdata/class/fail_instantiate_abstract_class_struct.carbon b/explorer/testdata/class/fail_instantiate_abstract_class_struct.carbon
index 489255ebbd0d..16c4e2db7ed1 100644
--- a/explorer/testdata/class/fail_instantiate_abstract_class_struct.carbon
+++ b/explorer/testdata/class/fail_instantiate_abstract_class_struct.carbon
@@ -11,7 +11,7 @@ abstract class C {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_instantiate_abstract_class_struct.carbon:[[@LINE+1]]: Cannot instantiate abstract class C
+  // CHECK:STDERR: COMPILATION ERROR: fail_instantiate_abstract_class_struct.carbon:[[@LINE+1]]: Cannot instantiate abstract class C
   var c: C = { .a = 1 };
   return 0;
 }
diff --git a/explorer/testdata/class/fail_invalid_subtyping.carbon b/explorer/testdata/class/fail_invalid_subtyping.carbon
index f5e8a0bd4c55..49db5c308dee 100644
--- a/explorer/testdata/class/fail_invalid_subtyping.carbon
+++ b/explorer/testdata/class/fail_invalid_subtyping.carbon
@@ -14,7 +14,7 @@ class D {
 
 fn Main() -> i32 {
   var d: D = {};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_invalid_subtyping.carbon:[[@LINE+1]]: type error in initializer of variable: 'class D*' is not implicitly convertible to 'class C*'
+  // CHECK:STDERR: COMPILATION ERROR: fail_invalid_subtyping.carbon:[[@LINE+1]]: type error in initializer of variable: 'class D*' is not implicitly convertible to 'class C*'
   var c: C* = &d;
   return 0;
 }
diff --git a/explorer/testdata/class/fail_member_call_before_typecheck.carbon b/explorer/testdata/class/fail_member_call_before_typecheck.carbon
index 508cd6ad7da8..0ae96cd2af23 100644
--- a/explorer/testdata/class/fail_member_call_before_typecheck.carbon
+++ b/explorer/testdata/class/fail_member_call_before_typecheck.carbon
@@ -10,7 +10,7 @@ class C {
   fn PickType() -> type { return i32; }
   // This is invalid even though `PickType` is defined earlier, because
   // checking of member bodies is deferred until after the class is completed.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_member_call_before_typecheck.carbon:[[@LINE+1]]: attempt to call function `PickType` that has not been fully type-checked
+  // CHECK:STDERR: COMPILATION ERROR: fail_member_call_before_typecheck.carbon:[[@LINE+1]]: attempt to call function `PickType` that has not been fully type-checked
   fn GetZero() -> PickType() { return 0; }
 }
 
diff --git a/explorer/testdata/class/fail_member_of_self.carbon b/explorer/testdata/class/fail_member_of_self.carbon
index dd56a0409f50..854fc1b48e62 100644
--- a/explorer/testdata/class/fail_member_of_self.carbon
+++ b/explorer/testdata/class/fail_member_of_self.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 class C {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_member_of_self.carbon:[[@LINE+1]]: incomplete type `class C` used in type of variable
+  // CHECK:STDERR: COMPILATION ERROR: fail_member_of_self.carbon:[[@LINE+1]]: incomplete type `class C` used in type of variable
   var m: Self;
 }
 
diff --git a/explorer/testdata/class/fail_method_deduced.carbon b/explorer/testdata/class/fail_method_deduced.carbon
index e68ea2004cdf..6bd5f56a56d1 100644
--- a/explorer/testdata/class/fail_method_deduced.carbon
+++ b/explorer/testdata/class/fail_method_deduced.carbon
@@ -15,7 +15,7 @@ fn H[T:! type](x: T) {}
 
 fn Main() -> i32 {
   H(C.F);
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_method_deduced.carbon:[[@LINE+1]]: member name G can only be used in a member access or alias
+  // CHECK:STDERR: COMPILATION ERROR: fail_method_deduced.carbon:[[@LINE+1]]: member name G can only be used in a member access or alias
   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 dda92e382235..50f67ed1f97b 100644
--- a/explorer/testdata/class/fail_method_from_class.carbon
+++ b/explorer/testdata/class/fail_method_from_class.carbon
@@ -20,6 +20,6 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 dca3564c6ef0..0659a430d7bb 100644
--- a/explorer/testdata/class/fail_method_in_var.carbon
+++ b/explorer/testdata/class/fail_method_in_var.carbon
@@ -13,7 +13,7 @@ class C {
 
 fn Main() -> i32 {
   var f: auto = C.F;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_method_in_var.carbon:[[@LINE+1]]: member name G can only be used in a member access or alias
+  // CHECK:STDERR: COMPILATION ERROR: fail_method_in_var.carbon:[[@LINE+1]]: member name G can only be used in a member access or alias
   var g: auto = C.G;
 
   return 0;
diff --git a/explorer/testdata/class/fail_override_virtual_with_non_virtual.carbon b/explorer/testdata/class/fail_override_virtual_with_non_virtual.carbon
index 6174d984aa81..68e64d120c49 100644
--- a/explorer/testdata/class/fail_override_virtual_with_non_virtual.carbon
+++ b/explorer/testdata/class/fail_override_virtual_with_non_virtual.carbon
@@ -11,7 +11,7 @@ base class A {
 }
 
 class B extends A {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_override_virtual_with_non_virtual.carbon:[[@LINE+1]]: Error declaring `Foo`: method is declared virtual in base class, use `impl` to override it.
+  // CHECK:STDERR: COMPILATION ERROR: fail_override_virtual_with_non_virtual.carbon:[[@LINE+1]]: Error declaring `Foo`: method is declared virtual in base class, use `impl` to override it.
   fn Foo[self: Self]() {}
 }
 
diff --git a/explorer/testdata/class/fail_qualified_method.carbon b/explorer/testdata/class/fail_qualified_method.carbon
index 10b0ac72f31b..b0fc424a8289 100644
--- a/explorer/testdata/class/fail_qualified_method.carbon
+++ b/explorer/testdata/class/fail_qualified_method.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 class Point {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_qualified_method.carbon:[[@LINE+1]]: qualified declaration names are not permitted in this context
+  // CHECK:STDERR: COMPILATION ERROR: fail_qualified_method.carbon:[[@LINE+1]]: qualified declaration names are not permitted in this context
   fn Point.F[self: Self]() {}
 }
 
diff --git a/explorer/testdata/class/fail_redeclare_virtual_method.carbon b/explorer/testdata/class/fail_redeclare_virtual_method.carbon
index b110bd72829b..0f7a21f1dc86 100644
--- a/explorer/testdata/class/fail_redeclare_virtual_method.carbon
+++ b/explorer/testdata/class/fail_redeclare_virtual_method.carbon
@@ -11,7 +11,7 @@ base class C {
 }
 
 class D extends C {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_redeclare_virtual_method.carbon:[[@LINE+1]]: Error declaring `Foo`: method is declared virtual in base class, use `impl` to override it.
+  // CHECK:STDERR: COMPILATION ERROR: fail_redeclare_virtual_method.carbon:[[@LINE+1]]: Error declaring `Foo`: method is declared virtual in base class, use `impl` to override it.
   virtual fn Foo[self:Self]() {}
 }
 
diff --git a/explorer/testdata/class/fail_return_method.carbon b/explorer/testdata/class/fail_return_method.carbon
index 454d76e3e856..98131eb84a20 100644
--- a/explorer/testdata/class/fail_return_method.carbon
+++ b/explorer/testdata/class/fail_return_method.carbon
@@ -12,7 +12,7 @@ class C {
 }
 
 fn ReturnF() -> auto { return C.F; }
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_return_method.carbon:[[@LINE+1]]: member name G can only be used in a member access or alias
+// CHECK:STDERR: COMPILATION ERROR: fail_return_method.carbon:[[@LINE+1]]: member name G can only be used in a member access or alias
 fn ReturnG() -> auto { return C.G; }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/class/fail_use_before_typecheck.carbon b/explorer/testdata/class/fail_use_before_typecheck.carbon
index d438c91d54f1..e488093f738e 100644
--- a/explorer/testdata/class/fail_use_before_typecheck.carbon
+++ b/explorer/testdata/class/fail_use_before_typecheck.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 class C {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_use_before_typecheck.carbon:[[@LINE+1]]: incomplete type `class C` used in member access
+  // CHECK:STDERR: COMPILATION ERROR: fail_use_before_typecheck.carbon:[[@LINE+1]]: incomplete type `class C` used in member access
   var n: if not C.WrapInStruct() then i32 else {.n: i32};
   fn WrapInStruct() -> bool { return true; }
 }
diff --git a/explorer/testdata/class/fail_virtual_class_function.carbon b/explorer/testdata/class/fail_virtual_class_function.carbon
index 3a795c86689d..3b8a2e49279c 100644
--- a/explorer/testdata/class/fail_virtual_class_function.carbon
+++ b/explorer/testdata/class/fail_virtual_class_function.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 class C {
   virtual fn Foo() -> i32 {
     return 1;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_virtual_class_function.carbon:[[@LINE+1]]: Error declaring `Foo`: class functions cannot be virtual.
+  // CHECK:STDERR: COMPILATION ERROR: fail_virtual_class_function.carbon:[[@LINE+1]]: Error declaring `Foo`: class functions cannot be virtual.
   }
 }
 
diff --git a/explorer/testdata/class/fail_virtual_method_absent.carbon b/explorer/testdata/class/fail_virtual_method_absent.carbon
index 503e5bf39d34..0ba4bc6605a3 100644
--- a/explorer/testdata/class/fail_virtual_method_absent.carbon
+++ b/explorer/testdata/class/fail_virtual_method_absent.carbon
@@ -17,6 +17,6 @@ fn Main() -> i32 {
   var bp: B* = &b;
   var ap: A* = bp;
   // Shouldn't look into the vtable for B.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/class/fail_virtual_method_absent.carbon:[[@LINE+1]]: class A does not have a field named Foo
+  // CHECK:STDERR: COMPILATION ERROR: fail_virtual_method_absent.carbon:[[@LINE+1]]: class A does not have a field named Foo
   return ap->Foo();
 }
diff --git a/explorer/testdata/comparison/fail_no_impl.carbon b/explorer/testdata/comparison/fail_no_impl.carbon
index 00eb38457a41..e56388f33abf 100644
--- a/explorer/testdata/comparison/fail_no_impl.carbon
+++ b/explorer/testdata/comparison/fail_no_impl.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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/fail_ambiguous_member.carbon b/explorer/testdata/constraint/fail_ambiguous_member.carbon
index a02f28760876..70bdcc7a88a0 100644
--- a/explorer/testdata/constraint/fail_ambiguous_member.carbon
+++ b/explorer/testdata/constraint/fail_ambiguous_member.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 interface A { fn F() -> i32; }
 interface B { fn F() -> i32; }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_ambiguous_member.carbon:[[@LINE+1]]: ambiguous member access, F found in interface A and interface B
+// CHECK:STDERR: COMPILATION ERROR: 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_combine_equality.carbon b/explorer/testdata/constraint/fail_combine_equality.carbon
index c748366c3cad..b4ac5bc4c3c2 100644
--- a/explorer/testdata/constraint/fail_combine_equality.carbon
+++ b/explorer/testdata/constraint/fail_combine_equality.carbon
@@ -11,7 +11,7 @@ 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:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_combine_equality.carbon:[[@LINE+1]]: member access, F not in interface I where T impls interface I and A == B and C == D and C == E and B == D
+  // CHECK:STDERR: COMPILATION ERROR: fail_combine_equality.carbon:[[@LINE+1]]: member access, F not in interface I where T impls interface I and A == B and C == D and C == E and B == D
   T.F();
 }
 
diff --git a/explorer/testdata/constraint/fail_dot_self_after_scope.carbon b/explorer/testdata/constraint/fail_dot_self_after_scope.carbon
index 04629f55011b..5973806e0cf6 100644
--- a/explorer/testdata/constraint/fail_dot_self_after_scope.carbon
+++ b/explorer/testdata/constraint/fail_dot_self_after_scope.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 interface FrobWith(T:! type) {}
 
 fn F[T:! FrobWith(.Self)]
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_dot_self_after_scope.carbon:[[@LINE+1]]: could not resolve '.Self'
+  // CHECK:STDERR: COMPILATION ERROR: 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 c5950f679482..c895f48699a5 100644
--- a/explorer/testdata/constraint/fail_dot_self_after_scope_2.carbon
+++ b/explorer/testdata/constraint/fail_dot_self_after_scope_2.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 interface FrobWith(T:! type) {}
 
 fn F[T:! FrobWith(.Self),
-     // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_dot_self_after_scope_2.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic binding `U`
+     // CHECK:STDERR: COMPILATION ERROR: fail_dot_self_after_scope_2.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic 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 9fa8f64f9ea5..02034f2e10a4 100644
--- a/explorer/testdata/constraint/fail_dot_self_not_in_scope.carbon
+++ b/explorer/testdata/constraint/fail_dot_self_not_in_scope.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_dot_self_not_in_scope.carbon:[[@LINE+1]]: could not resolve '.Self'
+// CHECK:STDERR: COMPILATION ERROR: 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 915cba6bde9c..2810acc0548d 100644
--- a/explorer/testdata/constraint/fail_infinite_self.carbon
+++ b/explorer/testdata/constraint/fail_infinite_self.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_infinite_self.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic binding `T`
+// CHECK:STDERR: COMPILATION ERROR: fail_infinite_self.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic 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 c68881f9dbce..00c5824c7889 100644
--- a/explorer/testdata/constraint/fail_infinite_self_ptr.carbon
+++ b/explorer/testdata/constraint/fail_infinite_self_ptr.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_infinite_self_ptr.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic binding `T`
+// CHECK:STDERR: COMPILATION ERROR: fail_infinite_self_ptr.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic binding `T`
 fn F[T:! .Self*]() {}
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/fail_missing_member.carbon b/explorer/testdata/constraint/fail_missing_member.carbon
index 2d77c9766dd9..bf74d831a303 100644
--- a/explorer/testdata/constraint/fail_missing_member.carbon
+++ b/explorer/testdata/constraint/fail_missing_member.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 interface A { fn F() -> i32; }
 interface B { fn G() -> i32; }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_missing_member.carbon:[[@LINE+1]]: member access, H not in interface A & interface B where T impls interface A and T impls interface B
+// CHECK:STDERR: COMPILATION ERROR: fail_missing_member.carbon:[[@LINE+1]]: member access, H not in interface A & interface B where T impls interface A and T impls interface B
 fn Get[T:! A & B](n: T) -> i32 { return n.H(); }
 
 impl i32 as A {
diff --git a/explorer/testdata/constraint/fail_non_type_self.carbon b/explorer/testdata/constraint/fail_non_type_self.carbon
index 0f3acfa34136..5caa8505f93d 100644
--- a/explorer/testdata/constraint/fail_non_type_self.carbon
+++ b/explorer/testdata/constraint/fail_non_type_self.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 class X(T:! type) {}
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_non_type_self.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic binding `T`
+// CHECK:STDERR: COMPILATION ERROR: fail_non_type_self.carbon:[[@LINE+1]]: `.Self` used in type of non-type generic 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 4f5f7a67a71a..e6693d6abffc 100644
--- a/explorer/testdata/constraint/fail_where_equals_different_types.carbon
+++ b/explorer/testdata/constraint/fail_where_equals_different_types.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 interface A {}
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_where_equals_different_types.carbon:[[@LINE+3]]: type mismatch between values in `where LHS == RHS`
+// CHECK:STDERR: COMPILATION ERROR: fail_where_equals_different_types.carbon:[[@LINE+3]]: type mismatch between values in `where LHS == RHS`
 // CHECK:STDERR:   LHS type: i32
 // CHECK:STDERR:   RHS type: type
 alias B = A where 4 == i32;
diff --git a/explorer/testdata/constraint/fail_where_impls_non_constraint.carbon b/explorer/testdata/constraint/fail_where_impls_non_constraint.carbon
index 2c5075fe8dcc..287a82dcf6c6 100644
--- a/explorer/testdata/constraint/fail_where_impls_non_constraint.carbon
+++ b/explorer/testdata/constraint/fail_where_impls_non_constraint.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 interface A {}
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_where_impls_non_constraint.carbon:[[@LINE+1]]: expected a constraint in expression after `impls`, found i32
+// CHECK:STDERR: COMPILATION ERROR: fail_where_impls_non_constraint.carbon:[[@LINE+1]]: expected a constraint in expression after `impls`, found i32
 alias B = A where i32 impls i32;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/fail_where_impls_non_type.carbon b/explorer/testdata/constraint/fail_where_impls_non_type.carbon
index 4deaf87a1e40..e65e8d138eeb 100644
--- a/explorer/testdata/constraint/fail_where_impls_non_type.carbon
+++ b/explorer/testdata/constraint/fail_where_impls_non_type.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 interface A {}
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_where_impls_non_type.carbon:[[@LINE+1]]: expression after `impls` does not resolve to a constraint, found i32
+// CHECK:STDERR: COMPILATION ERROR: fail_where_impls_non_type.carbon:[[@LINE+1]]: expression after `impls` does not resolve to a constraint, found i32
 alias B = A where i32 impls 5;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/constraint/fail_where_non_type_impls.carbon b/explorer/testdata/constraint/fail_where_non_type_impls.carbon
index 9a6feecd0b88..95259c36d26b 100644
--- a/explorer/testdata/constraint/fail_where_non_type_impls.carbon
+++ b/explorer/testdata/constraint/fail_where_non_type_impls.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 interface A {}
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/constraint/fail_where_non_type_impls.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
+// CHECK:STDERR: COMPILATION ERROR: fail_where_non_type_impls.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
 alias B = A where 4 impls A;
 
 fn Main() -> i32 { return 0; }
diff --git a/explorer/testdata/destructor/fail_addr.carbon b/explorer/testdata/destructor/fail_addr.carbon
index 7910f8fef221..63270a0f15fd 100644
--- a/explorer/testdata/destructor/fail_addr.carbon
+++ b/explorer/testdata/destructor/fail_addr.carbon
@@ -10,7 +10,7 @@ class A {
   destructor[addr self: Self*] {
     self->n += 1;
     Print("DESTRUCTOR A {0}", self->n);
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/destructor/fail_addr.carbon:[[@LINE+1]]: destructors currently don't support `addr self` bindings
+  // CHECK:STDERR: RUNTIME ERROR: fail_addr.carbon:[[@LINE+1]]: destructors currently don't support `addr self` bindings
   }
 
   var n: i32;
diff --git a/explorer/testdata/destructor/fail_delete_base_without_virtual_destructor.carbon b/explorer/testdata/destructor/fail_delete_base_without_virtual_destructor.carbon
index 4c37f482ceac..062aa77905d0 100644
--- a/explorer/testdata/destructor/fail_delete_base_without_virtual_destructor.carbon
+++ b/explorer/testdata/destructor/fail_delete_base_without_virtual_destructor.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: Deallocating a derived class from base class pointer requires a virtual destructor
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: Deallocating a derived class from base class pointer requires a virtual destructor
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon b/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon
index 3b49ae23ead0..9e4e9280ac35 100644
--- a/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon
+++ b/explorer/testdata/destructor/fail_multiple_destructor_declaration.carbon
@@ -12,7 +12,7 @@ class A{
     }
     destructor[self: Self]{
         Print("DESTRUCTOR A2 {0}",self.n);
-    // CHECK:STDERR: 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:[[@LINE-3]]
+    // CHECK:STDERR: COMPILATION ERROR: fail_multiple_destructor_declaration.carbon:[[@LINE+1]]: Duplicate name `destructor` also found at fail_multiple_destructor_declaration.carbon:[[@LINE-3]]
     }
     var n: i32;
 }
diff --git a/explorer/testdata/destructor/fail_override_abstract.carbon b/explorer/testdata/destructor/fail_override_abstract.carbon
index 8e294dd24990..45b06036e7ae 100644
--- a/explorer/testdata/destructor/fail_override_abstract.carbon
+++ b/explorer/testdata/destructor/fail_override_abstract.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 
 base class A {
-    // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/destructor/fail_override_abstract.carbon:[[@LINE+1]]: syntax error, unexpected DESTRUCTOR, expecting CLASS
+    // CHECK:STDERR: SYNTAX ERROR: fail_override_abstract.carbon:[[@LINE+1]]: syntax error, unexpected DESTRUCTOR, expecting CLASS
     abstract destructor[self: Self]{}
 }
 
diff --git a/explorer/testdata/destructor/fail_override_impl_none.carbon b/explorer/testdata/destructor/fail_override_impl_none.carbon
index b6bddc19582f..93f8284c37ce 100644
--- a/explorer/testdata/destructor/fail_override_impl_none.carbon
+++ b/explorer/testdata/destructor/fail_override_impl_none.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 
 base class A {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/destructor/fail_override_impl_none.carbon:[[@LINE+1]]: Error declaring destructor for `A`: cannot override a destructor that is not declared `virtual` in base class.
+    // CHECK:STDERR: COMPILATION ERROR: fail_override_impl_none.carbon:[[@LINE+1]]: Error declaring destructor for `A`: cannot override a destructor that is not declared `virtual` in base class.
     impl destructor[self: Self]{}
 }
 
diff --git a/explorer/testdata/destructor/fail_override_virtual_virtual.carbon b/explorer/testdata/destructor/fail_override_virtual_virtual.carbon
index 299dca74a317..263e09099dac 100644
--- a/explorer/testdata/destructor/fail_override_virtual_virtual.carbon
+++ b/explorer/testdata/destructor/fail_override_virtual_virtual.carbon
@@ -12,7 +12,7 @@ base class A {
 }
 
 class B extends A {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/destructor/fail_override_virtual_virtual.carbon:[[@LINE+1]]: Error declaring destructor for `B`: use `impl` to implement virtual destructor in child class.
+    // CHECK:STDERR: COMPILATION ERROR: fail_override_virtual_virtual.carbon:[[@LINE+1]]: Error declaring destructor for `B`: use `impl` to implement virtual destructor in child class.
     virtual destructor[self: Self]{}
 }
 
diff --git a/explorer/testdata/for/fail_convert.carbon b/explorer/testdata/for/fail_convert.carbon
index 24eeef6accbb..e4f948ffe104 100644
--- a/explorer/testdata/for/fail_convert.carbon
+++ b/explorer/testdata/for/fail_convert.carbon
@@ -20,7 +20,7 @@ fn Main() -> i32 {
   // representation to describe the conversion.
   for (x: IntLike in arr) {
     Print("{0}", x.n);
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/for/fail_convert.carbon:[[@LINE+3]]: type error in `for` pattern
+  // CHECK:STDERR: COMPILATION ERROR: fail_convert.carbon:[[@LINE+3]]: type error in `for` pattern
   // CHECK:STDERR: expected: i32
   // CHECK:STDERR: actual: class IntLike
   }
diff --git a/explorer/testdata/function/auto_return/fail_direct_recurse.carbon b/explorer/testdata/function/auto_return/fail_direct_recurse.carbon
index f78a7ab8ba35..7a0dafc9adc3 100644
--- a/explorer/testdata/function/auto_return/fail_direct_recurse.carbon
+++ b/explorer/testdata/function/auto_return/fail_direct_recurse.carbon
@@ -10,7 +10,7 @@ package ExplorerTest api;
 // used.
 fn Recurse(x: i32, do_recurse: bool) -> auto {
   if (do_recurse) {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/auto_return/fail_direct_recurse.carbon:[[@LINE+1]]: Function calls itself, but has a deduced return type
+    // CHECK:STDERR: COMPILATION ERROR: 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 791be6a47bb4..f9ad12bb276d 100644
--- a/explorer/testdata/function/auto_return/fail_multiple_returns.carbon
+++ b/explorer/testdata/function/auto_return/fail_multiple_returns.carbon
@@ -10,7 +10,7 @@ fn ComputeSum(x: i32, y: i32) -> auto {
   if (x == 0) {
     return x;
   } else if (y == 0) {
-    // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 d538b1bd1d5c..ac3f2ac4374d 100644
--- a/explorer/testdata/function/auto_return/fail_no_return.carbon
+++ b/explorer/testdata/function/auto_return/fail_no_return.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn NoReturn() -> auto {
-// CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 91ba9cda61b2..372703f44228 100644
--- a/explorer/testdata/function/auto_return/fail_separate_decl.carbon
+++ b/explorer/testdata/function/auto_return/fail_separate_decl.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 // This declaration is not allowed.
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/auto_return/fail_separate_decl.carbon:[[@LINE+1]]: Function declaration has deduced return type but no body
+// CHECK:STDERR: COMPILATION ERROR: fail_separate_decl.carbon:[[@LINE+1]]: Function declaration has deduced return type but no body
 fn ComputeSum(x: i32, y: i32) -> auto;
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/function/fail_call_undefined.carbon b/explorer/testdata/function/fail_call_undefined.carbon
index 528b851ee548..81bedf94abd1 100644
--- a/explorer/testdata/function/fail_call_undefined.carbon
+++ b/explorer/testdata/function/fail_call_undefined.carbon
@@ -9,6 +9,6 @@ package ExplorerTest api;
 fn F() -> i32;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/function/fail_call_undefined.carbon:[[@LINE+1]]: attempt to call function `F` that has not been defined
+  // CHECK:STDERR: RUNTIME ERROR: fail_call_undefined.carbon:[[@LINE+1]]: attempt to call function `F` that has not been defined
   return F();
 }
diff --git a/explorer/testdata/function/fail_call_with_tuple.carbon b/explorer/testdata/function/fail_call_with_tuple.carbon
index 69f662be6c51..dbeaac11b776 100644
--- a/explorer/testdata/function/fail_call_with_tuple.carbon
+++ b/explorer/testdata/function/fail_call_with_tuple.carbon
@@ -11,6 +11,6 @@ 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:STDERR: 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:STDERR: COMPILATION ERROR: 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 b7ae5c207d3e..51d73f38b8d7 100644
--- a/explorer/testdata/function/fail_invalid_fnty.carbon
+++ b/explorer/testdata/function/fail_invalid_fnty.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/fail_invalid_fnty.carbon:[[@LINE+2]]: type error in `-`:
+// CHECK:STDERR: COMPILATION ERROR: fail_invalid_fnty.carbon:[[@LINE+2]]: type error in `-`:
 // CHECK:STDERR: could not find implementation of interface Negate for bool
 fn f(g: __Fn(-true) -> true) {
 }
diff --git a/explorer/testdata/function/fail_main_with_parameters.carbon b/explorer/testdata/function/fail_main_with_parameters.carbon
index d7c68b66cb80..633fd797fb98 100644
--- a/explorer/testdata/function/fail_main_with_parameters.carbon
+++ b/explorer/testdata/function/fail_main_with_parameters.carbon
@@ -8,5 +8,5 @@ package ExplorerTest api;
 
 fn Main(i: i32) -> i32 {
     return 0;
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/fail_main_with_parameters.carbon:[[@LINE+1]]: `Main` must not take any parameters
+// CHECK:STDERR: COMPILATION ERROR: fail_main_with_parameters.carbon:[[@LINE+1]]: `Main` must not take any parameters
 }
diff --git a/explorer/testdata/function/fail_match_no_return.carbon b/explorer/testdata/function/fail_match_no_return.carbon
index 409d21ef907a..33a95ac18399 100644
--- a/explorer/testdata/function/fail_match_no_return.carbon
+++ b/explorer/testdata/function/fail_match_no_return.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: i32 = 0;
   match(0) {
-    // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 ab0557a64495..c18f950122e3 100644
--- a/explorer/testdata/function/fail_match_partial_return.carbon
+++ b/explorer/testdata/function/fail_match_partial_return.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: i32 = 0;
   match (0) {
-    // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 ec4a76a6573a..604b2079e60f 100644
--- a/explorer/testdata/function/fail_non_exhaustive_match.carbon
+++ b/explorer/testdata/function/fail_non_exhaustive_match.carbon
@@ -11,5 +11,5 @@ fn Main() -> i32 {
   match (n) {
     case 1 => { return 0; }
   }
-// CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 ea968404f022..537a3be6f75c 100644
--- a/explorer/testdata/function/fail_parameter_type.carbon
+++ b/explorer/testdata/function/fail_parameter_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 // 42 cannot be used as the type of a parameter.
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/fail_parameter_type.carbon:[[@LINE+1]]: type error in type of name binding: 'i32' is not implicitly convertible to 'type'
+// CHECK:STDERR: COMPILATION ERROR: fail_parameter_type.carbon:[[@LINE+1]]: type error in type of name binding: 'i32' is not implicitly convertible to 'type'
 fn f(x: 42) -> i32 {
   return x - 1;
 }
diff --git a/explorer/testdata/function/fail_parameter_type_only.carbon b/explorer/testdata/function/fail_parameter_type_only.carbon
index 6a547277b29d..ce4386ad96ad 100644
--- a/explorer/testdata/function/fail_parameter_type_only.carbon
+++ b/explorer/testdata/function/fail_parameter_type_only.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/fail_parameter_type_only.carbon:[[@LINE+1]]: An irrefutable pattern is required, but `i32` is refutable.
+// CHECK:STDERR: COMPILATION ERROR: fail_parameter_type_only.carbon:[[@LINE+1]]: An irrefutable pattern is required, but `i32` is refutable.
 fn f(x: i32, i32) {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/function/fail_recurse_before_typecheck.carbon b/explorer/testdata/function/fail_recurse_before_typecheck.carbon
index 5e0298e28a49..d8adc45b3640 100644
--- a/explorer/testdata/function/fail_recurse_before_typecheck.carbon
+++ b/explorer/testdata/function/fail_recurse_before_typecheck.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn T() -> type {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/fail_recurse_before_typecheck.carbon:[[@LINE+1]]: attempt to call function `T` that has not been fully type-checked
+  // CHECK:STDERR: COMPILATION ERROR: fail_recurse_before_typecheck.carbon:[[@LINE+1]]: attempt to call function `T` that has not been fully type-checked
   var v: T() = 0;
   return i32;
 }
diff --git a/explorer/testdata/function/fail_recurse_in_return_type.carbon b/explorer/testdata/function/fail_recurse_in_return_type.carbon
index 36ea1c6a50dc..01e7c8454df9 100644
--- a/explorer/testdata/function/fail_recurse_in_return_type.carbon
+++ b/explorer/testdata/function/fail_recurse_in_return_type.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/fail_recurse_in_return_type.carbon:[[@LINE+1]]: 'T' is not usable until after it has been completely declared
+// CHECK:STDERR: COMPILATION ERROR: fail_recurse_in_return_type.carbon:[[@LINE+1]]: 'T' is not usable until after it has been completely declared
 fn T() -> T() { return i32; }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/function/fail_return_call_has_invalid_body.carbon b/explorer/testdata/function/fail_return_call_has_invalid_body.carbon
index 66dba1840d23..353d3fb1afde 100644
--- a/explorer/testdata/function/fail_return_call_has_invalid_body.carbon
+++ b/explorer/testdata/function/fail_return_call_has_invalid_body.carbon
@@ -7,7 +7,7 @@
 package EmptyIdentifier impl;
 
 fn apply[T:! type, U:! type](f: T, EmptyIdentifier: U) {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/fail_return_call_has_invalid_body.carbon:[[@LINE+1]]: only arrays and tuples can be indexed, found bool
+  // CHECK:STDERR: COMPILATION ERROR: fail_return_call_has_invalid_body.carbon:[[@LINE+1]]: only arrays and tuples can be indexed, found bool
   match (true[true]) {}
 }
 
diff --git a/explorer/testdata/function/fail_var_type_is_call.carbon b/explorer/testdata/function/fail_var_type_is_call.carbon
index 1c9e187bc016..42d63327824e 100644
--- a/explorer/testdata/function/fail_var_type_is_call.carbon
+++ b/explorer/testdata/function/fail_var_type_is_call.carbon
@@ -11,7 +11,7 @@ fn test() -> i32 {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/function/fail_var_type_is_call.carbon:[[@LINE+1]]: type error in type of name binding: 'i32' is not implicitly convertible to 'type'
+  // CHECK:STDERR: COMPILATION ERROR: fail_var_type_is_call.carbon:[[@LINE+1]]: type error in type of name binding: 'i32' is not implicitly convertible to 'type'
   var x: test() = 1;
   return 0;
 }
diff --git a/explorer/testdata/generic_class/fail_args_mismatch.carbon b/explorer/testdata/generic_class/fail_args_mismatch.carbon
index 599c4efa4c0b..a31042514a07 100644
--- a/explorer/testdata/generic_class/fail_args_mismatch.carbon
+++ b/explorer/testdata/generic_class/fail_args_mismatch.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 class Point(T:! type) {
   // Point(T, T) does not match class declaration
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 6f5064742a59..37f69567950e 100644
--- a/explorer/testdata/generic_class/fail_argument_deduction.carbon
+++ b/explorer/testdata/generic_class/fail_argument_deduction.carbon
@@ -18,7 +18,7 @@ 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:STDERR: COMPILATION ERROR: explorer/testdata/generic_class/fail_argument_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! type:
+  // CHECK:STDERR: COMPILATION ERROR: fail_argument_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! type:
   // CHECK:STDERR:   i32
   // CHECK:STDERR:   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 f95ce5ec41d3..2b31eeac6b3f 100644
--- a/explorer/testdata/generic_class/fail_bad_parameter_type.carbon
+++ b/explorer/testdata/generic_class/fail_bad_parameter_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 class Point(T:! i32) {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_class/fail_bad_parameter_type.carbon:[[@LINE+1]]: type error in type of name binding: 'i32' is not implicitly convertible to 'type'
+  // CHECK:STDERR: COMPILATION ERROR: fail_bad_parameter_type.carbon:[[@LINE+1]]: type error in type of name binding: 'i32' is not implicitly convertible to 'type'
   fn Origin(zero: T) -> Point(T) {
     return {.x = zero, .y = zero};
   }
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 d3fda3ed2f6f..13c4f8b56ad1 100644
--- a/explorer/testdata/generic_class/fail_field_access_on_generic.carbon
+++ b/explorer/testdata/generic_class/fail_field_access_on_generic.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn BadSimpleMemberAccess[T:! type](a: T) -> T {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_class/fail_field_access_on_generic.carbon:[[@LINE+1]]: member access in unconstrained type
+  // CHECK:STDERR: COMPILATION ERROR: 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 ca1802b013e2..f34df1d7e132 100644
--- a/explorer/testdata/generic_class/fail_generic_class_arg.carbon
+++ b/explorer/testdata/generic_class/fail_generic_class_arg.carbon
@@ -16,7 +16,7 @@ class Point(T:! type) {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 01bb30e13a3d..9cd776e9234a 100644
--- a/explorer/testdata/generic_class/fail_generic_in_pattern.carbon
+++ b/explorer/testdata/generic_class/fail_generic_in_pattern.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var t: auto = 5;
   match (t) {
-    // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 2076fcd34459..022805bab42c 100644
--- a/explorer/testdata/generic_class/fail_instantiate_non_generic.carbon
+++ b/explorer/testdata/generic_class/fail_instantiate_non_generic.carbon
@@ -15,7 +15,7 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_class/fail_instantiate_non_generic.carbon:[[@LINE+1]]: in call `Point(i32)`, expected callee to be a function, found `type`
+  // CHECK:STDERR: COMPILATION ERROR: fail_instantiate_non_generic.carbon:[[@LINE+1]]: in call `Point(i32)`, expected callee to be a function, found `type`
   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 d4419cd240ef..11bcd680c330 100644
--- a/explorer/testdata/generic_class/fail_no_args.carbon
+++ b/explorer/testdata/generic_class/fail_no_args.carbon
@@ -12,7 +12,7 @@ class Point(T:! type) {
   }
 
   // Error: wrote `Point` instead of `Point(T)`, `Point` by itself is not a type.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_class/fail_no_args.carbon:[[@LINE+1]]: 'Point' must be given an argument list
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_args.carbon:[[@LINE+1]]: 'Point' must be given an argument list
   fn GetX[self: Point]() -> T {
     return self.x;
   }
diff --git a/explorer/testdata/generic_class/fail_point_equal.carbon b/explorer/testdata/generic_class/fail_point_equal.carbon
index fa9a621bdcc8..181d401a183c 100644
--- a/explorer/testdata/generic_class/fail_point_equal.carbon
+++ b/explorer/testdata/generic_class/fail_point_equal.carbon
@@ -13,7 +13,7 @@ class Point(T:! type) {
 
 fn Main() -> i32 {
   var p: Point(i32) = {.x = 0, .y = 0};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_class/fail_point_equal.carbon:[[@LINE+1]]: type error in initializer of variable: 'class Point(T = i32)' is not implicitly convertible to 'class Point(T = bool)'
+  // CHECK:STDERR: COMPILATION ERROR: fail_point_equal.carbon:[[@LINE+1]]: type error in initializer of variable: '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 71219cc1fcfd..b42172978a4e 100644
--- a/explorer/testdata/generic_class/fail_return_type_is_type.carbon
+++ b/explorer/testdata/generic_class/fail_return_type_is_type.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 class Point(T:! type) {
   // The return type should be Point(T). Point by itself is not a type.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_class/fail_return_type_is_type.carbon:[[@LINE+1]]: 'Point' must be given an argument list
+  // CHECK:STDERR: COMPILATION ERROR: fail_return_type_is_type.carbon:[[@LINE+1]]: 'Point' must be given an argument list
   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 a03425a5619a..a8e73e6a880a 100644
--- a/explorer/testdata/generic_class/fail_self_with_arg.carbon
+++ b/explorer/testdata/generic_class/fail_self_with_arg.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 class Point(T:! type) {
 
   // Error: wrote `Self(T)` instead of `Self`.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_class/fail_self_with_arg.carbon:[[@LINE+1]]: in call `Self(T)`, expected callee to be a function, found `type`
+  // CHECK:STDERR: COMPILATION ERROR: fail_self_with_arg.carbon:[[@LINE+1]]: in call `Self(T)`, expected callee to be a function, found `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 3a493d8a0149..b51c326a7da6 100644
--- a/explorer/testdata/generic_class/fail_two_arg_lists.carbon
+++ b/explorer/testdata/generic_class/fail_two_arg_lists.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 class Point(T:! type) {
-  // CHECK:STDERR: 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 `type`
+  // CHECK:STDERR: COMPILATION ERROR: fail_two_arg_lists.carbon:[[@LINE+1]]: in call `Point(T)(T)`, expected callee to be a function, found `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 2b1c4d083386..2bbd923eba21 100644
--- a/explorer/testdata/generic_class/fail_value_param_mismatch.carbon
+++ b/explorer/testdata/generic_class/fail_value_param_mismatch.carbon
@@ -12,7 +12,7 @@ fn F(x: HasI32Param(1)) {}
 
 fn Main() -> i32 {
   var n: HasI32Param(0) = {};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_class/fail_value_param_mismatch.carbon:[[@LINE+1]]: mismatch in non-deduced values, `0` != `1`
+  // CHECK:STDERR: COMPILATION ERROR: fail_value_param_mismatch.carbon:[[@LINE+1]]: mismatch in non-deduced values, `0` != `1`
   F(n);
   return 0;
 }
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 249bfcdb8fd3..b5c4b067aab5 100644
--- a/explorer/testdata/generic_function/fail_implicit_conversion_extra_field.carbon
+++ b/explorer/testdata/generic_function/fail_implicit_conversion_extra_field.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn Bad[T:! type](x: {.a: i32, .b: T}) {}
 
 fn Main() -> i32 {
-  // CHECK:STDERR: 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}`
+  // CHECK:STDERR: COMPILATION ERROR: fail_implicit_conversion_extra_field.carbon:[[@LINE+1]]: mismatch in field names, source field `c` not in destination type `{.a: i32, .b: T}`
   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 1798bd3419ec..8d49d48979e3 100644
--- a/explorer/testdata/generic_function/fail_implicit_conversion_missing_field.carbon
+++ b/explorer/testdata/generic_function/fail_implicit_conversion_missing_field.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn Bad[T:! type](x: {.a: i32, .b: T}) {}
 
 fn Main() -> i32 {
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 11e8d3651cc0..7a1cef81f041 100644
--- a/explorer/testdata/generic_function/fail_missing_exclam.carbon
+++ b/explorer/testdata/generic_function/fail_missing_exclam.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/generic_function/fail_missing_exclam.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
+// CHECK:STDERR: SYNTAX ERROR: 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 d9515e38503f..af981669ec17 100644
--- a/explorer/testdata/generic_function/fail_not_addable.carbon
+++ b/explorer/testdata/generic_function/fail_not_addable.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn id[T:! type](x: T) -> T {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_function/fail_not_addable.carbon:[[@LINE+2]]: type error in `+`:
+  // CHECK:STDERR: COMPILATION ERROR: fail_not_addable.carbon:[[@LINE+2]]: type error in `+`:
   // CHECK:STDERR: could not find implementation of interface AddWith(U = i32) for T
   return x + 0;
 }
diff --git a/explorer/testdata/generic_function/fail_not_type.carbon b/explorer/testdata/generic_function/fail_not_type.carbon
index ba960c7e0f3b..173cafc5fb5d 100644
--- a/explorer/testdata/generic_function/fail_not_type.carbon
+++ b/explorer/testdata/generic_function/fail_not_type.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_function/fail_not_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
+// CHECK:STDERR: COMPILATION ERROR: fail_not_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
 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 3d7bc6f626ea..98c607accf9a 100644
--- a/explorer/testdata/generic_function/fail_type_deduction_mismatch.carbon
+++ b/explorer/testdata/generic_function/fail_type_deduction_mismatch.carbon
@@ -11,7 +11,7 @@ fn fst[T:! type](x: T, y: T) -> T {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_function/fail_type_deduction_mismatch.carbon:[[@LINE+3]]: deduced multiple different values for T:! type:
+  // CHECK:STDERR: COMPILATION ERROR: fail_type_deduction_mismatch.carbon:[[@LINE+3]]: deduced multiple different values for T:! type:
   // CHECK:STDERR:   i32
   // CHECK:STDERR:   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 8ee375c787b5..abed628d3e54 100644
--- a/explorer/testdata/generic_function/fail_type_deduction_unused.carbon
+++ b/explorer/testdata/generic_function/fail_type_deduction_unused.carbon
@@ -11,6 +11,6 @@ fn id[T:! type](x: i32) -> i32 {
 }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/generic_function/fail_type_deduction_unused.carbon:[[@LINE+1]]: could not deduce type argument for type parameter T in call
+  // CHECK:STDERR: COMPILATION ERROR: fail_type_deduction_unused.carbon:[[@LINE+1]]: could not deduce type argument for type parameter T in call
   return id(0);
 }
diff --git a/explorer/testdata/generic_function/fail_type_only.carbon b/explorer/testdata/generic_function/fail_type_only.carbon
index d468428c6482..472a8f4d1152 100644
--- a/explorer/testdata/generic_function/fail_type_only.carbon
+++ b/explorer/testdata/generic_function/fail_type_only.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 class C {}
 
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/generic_function/fail_type_only.carbon:[[@LINE+1]]: syntax error, unexpected RIGHT_SQUARE_BRACKET, expecting COLON
+// CHECK:STDERR: SYNTAX ERROR: fail_type_only.carbon:[[@LINE+1]]: syntax error, unexpected RIGHT_SQUARE_BRACKET, expecting COLON
 fn f[x:! i32, addr C]() {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon b/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon
index c523b1cc70b9..4e56978a25fb 100644
--- a/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon
+++ b/explorer/testdata/generic_function/fail_wrong_variable_substituation.carbon
@@ -13,7 +13,7 @@ fn Get[T:! ()](n: T) -> i32 {  return 2; }
 
 fn Main() -> i32 {
   var x : X = {};
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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/impl/fail_bad_member_kind.carbon b/explorer/testdata/impl/fail_bad_member_kind.carbon
index b3eb0b6df813..b641e10b00c1 100644
--- a/explorer/testdata/impl/fail_bad_member_kind.carbon
+++ b/explorer/testdata/impl/fail_bad_member_kind.carbon
@@ -12,7 +12,7 @@ interface A {
 }
 
 external impl i32 as A {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/impl/fail_bad_member_kind.carbon:[[@LINE+1]]: syntax error, unexpected CLASS
+  // CHECK:STDERR: SYNTAX ERROR: fail_bad_member_kind.carbon:[[@LINE+1]]: syntax error, unexpected CLASS
   class T {}
 }
 
diff --git a/explorer/testdata/impl/fail_impl_as.carbon b/explorer/testdata/impl/fail_impl_as.carbon
index a7f2c02f7302..1f44cb8ced89 100644
--- a/explorer/testdata/impl/fail_impl_as.carbon
+++ b/explorer/testdata/impl/fail_impl_as.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl/fail_impl_as.carbon:[[@LINE+1]]: expected a constraint in impl declaration, found i32
+// CHECK:STDERR: COMPILATION ERROR: fail_impl_as.carbon:[[@LINE+1]]: expected a constraint in impl declaration, found 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 dcf299b735d2..c5fdb070db3b 100644
--- a/explorer/testdata/impl/fail_impl_as_non_interface.carbon
+++ b/explorer/testdata/impl/fail_impl_as_non_interface.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl/fail_impl_as_non_interface.carbon:[[@LINE+1]]: expected a constraint in impl declaration, found String
+// CHECK:STDERR: COMPILATION ERROR: fail_impl_as_non_interface.carbon:[[@LINE+1]]: expected a constraint in impl declaration, found 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 ea3f6d9cfaac..358b0d06501b 100644
--- a/explorer/testdata/impl/fail_impl_as_not_constraint.carbon
+++ b/explorer/testdata/impl/fail_impl_as_not_constraint.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl/fail_impl_as_not_constraint.carbon:[[@LINE+1]]: expected a constraint in impl declaration, found i32
+// CHECK:STDERR: COMPILATION ERROR: fail_impl_as_not_constraint.carbon:[[@LINE+1]]: expected a constraint in impl declaration, found 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 c98b3ef6d288..c6f89363485d 100644
--- a/explorer/testdata/impl/fail_impl_as_parameterized.carbon
+++ b/explorer/testdata/impl/fail_impl_as_parameterized.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 interface Vector(Scalar:! type) {
 }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl/fail_impl_as_parameterized.carbon:[[@LINE+1]]: 'Vector' must be given an argument list
+// CHECK:STDERR: COMPILATION ERROR: fail_impl_as_parameterized.carbon:[[@LINE+1]]: 'Vector' must be given an argument list
 external impl i32 as Vector {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/impl/fail_impl_redefinition.carbon b/explorer/testdata/impl/fail_impl_redefinition.carbon
index 4c7f4050d0d2..3302e7445352 100644
--- a/explorer/testdata/impl/fail_impl_redefinition.carbon
+++ b/explorer/testdata/impl/fail_impl_redefinition.carbon
@@ -33,7 +33,7 @@ external impl Point as Vector {
   fn Scale[self: Point](v: i32) -> Point {
       return {.x = self.x * v, .y = self.y * v};
   }
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl/fail_impl_redefinition.carbon:[[@LINE+1]]: ambiguous implementations of interface Vector for class Point
+// CHECK:STDERR: COMPILATION ERROR: fail_impl_redefinition.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_nondeducible_parameter.carbon b/explorer/testdata/impl/fail_nondeducible_parameter.carbon
index 4b7f1f6889ae..242f0c2fe97e 100644
--- a/explorer/testdata/impl/fail_nondeducible_parameter.carbon
+++ b/explorer/testdata/impl/fail_nondeducible_parameter.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 interface A(T:! type) {}
 interface B {}
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl/fail_nondeducible_parameter.carbon:[[@LINE+1]]: parameter `T:! type` is not deducible from `impl i32 as interface B`
+// CHECK:STDERR: COMPILATION ERROR: 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 322fc1bd3ed8..2e75c5a0b62e 100644
--- a/explorer/testdata/impl/fail_param_interface_in_impl.carbon
+++ b/explorer/testdata/impl/fail_param_interface_in_impl.carbon
@@ -17,7 +17,7 @@ fn Main() -> i32 {
   let n: i32 = 0;
   CheckSimilar(true, false);
   CheckSimilar(true, n);
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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_unmet_impls_constraint.carbon b/explorer/testdata/impl/fail_unmet_impls_constraint.carbon
index a12877176063..fdc857173859 100644
--- a/explorer/testdata/impl/fail_unmet_impls_constraint.carbon
+++ b/explorer/testdata/impl/fail_unmet_impls_constraint.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 interface A {}
 interface B {}
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl/fail_unmet_impls_constraint.carbon:[[@LINE+1]]: could not find implementation of interface B for i32
+// CHECK:STDERR: COMPILATION ERROR: fail_unmet_impls_constraint.carbon:[[@LINE+1]]: could not find implementation of interface B for i32
 external impl i32 as A where i32 impls B {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/impl_match/fail_self_recurse.carbon b/explorer/testdata/impl_match/fail_self_recurse.carbon
index b2ab885243cd..d3c088298052 100644
--- a/explorer/testdata/impl_match/fail_self_recurse.carbon
+++ b/explorer/testdata/impl_match/fail_self_recurse.carbon
@@ -13,7 +13,7 @@ impl forall [T:! type where .Self* impls Foo] T as Foo {}
 fn F[T:! Foo](x: T) {}
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl_match/fail_self_recurse.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
+  // CHECK:STDERR: COMPILATION ERROR: fail_self_recurse.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
   // CHECK:STDERR:   outer match: i32 as interface Foo
   // CHECK:STDERR:   inner match: i32* as interface Foo
   F(0);
diff --git a/explorer/testdata/impl_match/fail_self_recurse_without_match_first.carbon b/explorer/testdata/impl_match/fail_self_recurse_without_match_first.carbon
index 6c1b51317927..70dbfaeafc1e 100644
--- a/explorer/testdata/impl_match/fail_self_recurse_without_match_first.carbon
+++ b/explorer/testdata/impl_match/fail_self_recurse_without_match_first.carbon
@@ -17,7 +17,7 @@ fn Main() -> i32 {
   // When checking the second impl, we recursively look for a match for
   // i32* as Foo, which considers the second impl again, even though the first
   // impl would match.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl_match/fail_self_recurse_without_match_first.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
+  // CHECK:STDERR: COMPILATION ERROR: fail_self_recurse_without_match_first.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
   // CHECK:STDERR:   outer match: i32 as interface Foo
   // CHECK:STDERR:   inner match: i32* as interface Foo
   F(0);
diff --git a/explorer/testdata/impl_match/fail_simple_self_recurse.carbon b/explorer/testdata/impl_match/fail_simple_self_recurse.carbon
index b7c0e1e73680..a3e9db97bf2b 100644
--- a/explorer/testdata/impl_match/fail_simple_self_recurse.carbon
+++ b/explorer/testdata/impl_match/fail_simple_self_recurse.carbon
@@ -13,7 +13,7 @@ impl forall [T:! Foo] T as Foo {}
 fn F[T:! Foo](x: T) {}
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl_match/fail_simple_self_recurse.carbon:[[@LINE+1]]: impl matching for i32 as interface Foo recursively performed a match for the same type and interface
+  // CHECK:STDERR: COMPILATION ERROR: fail_simple_self_recurse.carbon:[[@LINE+1]]: impl matching for i32 as interface Foo recursively performed a match for the same type and interface
   F(0);
   return 0;
 }
diff --git a/explorer/testdata/impl_match/fail_struct_recurse.carbon b/explorer/testdata/impl_match/fail_struct_recurse.carbon
index 57bdb1d31813..7e4d4a69c494 100644
--- a/explorer/testdata/impl_match/fail_struct_recurse.carbon
+++ b/explorer/testdata/impl_match/fail_struct_recurse.carbon
@@ -13,7 +13,7 @@ impl forall [T:! type where {.a: .Self} impls Foo] T as Foo {}
 fn F[T:! Foo](x: T) {}
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl_match/fail_struct_recurse.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
+  // CHECK:STDERR: COMPILATION ERROR: fail_struct_recurse.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
   // CHECK:STDERR:   outer match: i32 as interface Foo
   // CHECK:STDERR:   inner match: {.a: i32} as interface Foo
   F(0);
diff --git a/explorer/testdata/impl_match/fail_three_step_recurse.carbon b/explorer/testdata/impl_match/fail_three_step_recurse.carbon
index b24ce9aa60dc..17f49ccd863d 100644
--- a/explorer/testdata/impl_match/fail_three_step_recurse.carbon
+++ b/explorer/testdata/impl_match/fail_three_step_recurse.carbon
@@ -17,7 +17,7 @@ impl forall [T:! type where .Self* impls C] T as A {}
 fn F[T:! A](x: T) {}
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl_match/fail_three_step_recurse.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
+  // CHECK:STDERR: COMPILATION ERROR: fail_three_step_recurse.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
   // CHECK:STDERR:   outer match: i32 as interface A
   // CHECK:STDERR:   inner match: i32*** as interface A
   F(0);
diff --git a/explorer/testdata/impl_match/fail_tuple_recurse.carbon b/explorer/testdata/impl_match/fail_tuple_recurse.carbon
index f8c6658d5f2f..69dafdf0ff8e 100644
--- a/explorer/testdata/impl_match/fail_tuple_recurse.carbon
+++ b/explorer/testdata/impl_match/fail_tuple_recurse.carbon
@@ -13,7 +13,7 @@ impl forall [T:! type where (.Self,) impls Foo] T as Foo {}
 fn F[T:! Foo](x: T) {}
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/impl_match/fail_tuple_recurse.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
+  // CHECK:STDERR: COMPILATION ERROR: fail_tuple_recurse.carbon:[[@LINE+3]]: impl matching recursively performed a more complex match using the same impl
   // CHECK:STDERR:   outer match: i32 as interface Foo
   // CHECK:STDERR:   inner match: (i32,) as interface Foo
   F(0);
diff --git a/explorer/testdata/import/fail_order.carbon b/explorer/testdata/import/fail_order.carbon
index 26048ce057d9..24065c7ffc76 100644
--- a/explorer/testdata/import/fail_order.carbon
+++ b/explorer/testdata/import/fail_order.carbon
@@ -10,5 +10,5 @@ fn Main() -> i32 {
   return 0;
 }
 
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/import/fail_order.carbon:[[@LINE+1]]: syntax error, unexpected IMPORT, expecting END_OF_FILE
+// CHECK:STDERR: SYNTAX ERROR: fail_order.carbon:[[@LINE+1]]: syntax error, unexpected IMPORT, expecting END_OF_FILE
 import ExplorerTest library "Nonexistent";
diff --git a/explorer/testdata/interface/fail_bad_member_kind.carbon b/explorer/testdata/interface/fail_bad_member_kind.carbon
index ccc008d80aae..2367d3ecdbd3 100644
--- a/explorer/testdata/interface/fail_bad_member_kind.carbon
+++ b/explorer/testdata/interface/fail_bad_member_kind.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 interface Bad {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/interface/fail_bad_member_kind.carbon:[[@LINE+1]]: syntax error, unexpected VAR
+  // CHECK:STDERR: SYNTAX ERROR: fail_bad_member_kind.carbon:[[@LINE+1]]: syntax error, unexpected VAR
   var V: i32;
 }
 
diff --git a/explorer/testdata/interface/fail_extends_not_constraint.carbon b/explorer/testdata/interface/fail_extends_not_constraint.carbon
index 1ea0c7cebd21..a7f18f15357e 100644
--- a/explorer/testdata/interface/fail_extends_not_constraint.carbon
+++ b/explorer/testdata/interface/fail_extends_not_constraint.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 interface Vector {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_extends_not_constraint.carbon:[[@LINE+1]]: expected a constraint in extends declaration, found i32
+  // CHECK:STDERR: COMPILATION ERROR: fail_extends_not_constraint.carbon:[[@LINE+1]]: expected a constraint in extends declaration, found i32
   extends i32;
 }
 
diff --git a/explorer/testdata/interface/fail_external_impl_omit_self.carbon b/explorer/testdata/interface/fail_external_impl_omit_self.carbon
index 709979a51604..22b31eaff477 100644
--- a/explorer/testdata/interface/fail_external_impl_omit_self.carbon
+++ b/explorer/testdata/interface/fail_external_impl_omit_self.carbon
@@ -17,7 +17,7 @@ class Point {
 }
 
 // Error: need to specify which type implementing `Vector` for.
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_external_impl_omit_self.carbon:[[@LINE+1]]: could not resolve 'Self'
+// CHECK:STDERR: COMPILATION ERROR: fail_external_impl_omit_self.carbon:[[@LINE+1]]: could not resolve 'Self'
 external impl as Vector {
   fn Add[self: Point](b: Point) -> Point {
     return {.x = self.x + b.x, .y = self.y + b.y};
diff --git a/explorer/testdata/interface/fail_external_impl_self.carbon b/explorer/testdata/interface/fail_external_impl_self.carbon
index c71f4745ab53..1cc91318d6ad 100644
--- a/explorer/testdata/interface/fail_external_impl_self.carbon
+++ b/explorer/testdata/interface/fail_external_impl_self.carbon
@@ -16,7 +16,7 @@ class Point {
   var y: i32;
 }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_external_impl_self.carbon:[[@LINE+1]]: could not resolve 'Self'
+// CHECK:STDERR: COMPILATION ERROR: fail_external_impl_self.carbon:[[@LINE+1]]: could not resolve 'Self'
 external impl Self as Vector {
   fn Add[self: Point](b: Point) -> Point {
     return {.x = self.x + b.x, .y = self.y + b.y};
diff --git a/explorer/testdata/interface/fail_impl_as_not_constraint.carbon b/explorer/testdata/interface/fail_impl_as_not_constraint.carbon
index f756615fcc27..8b074fad424b 100644
--- a/explorer/testdata/interface/fail_impl_as_not_constraint.carbon
+++ b/explorer/testdata/interface/fail_impl_as_not_constraint.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 interface Vector {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_impl_as_not_constraint.carbon:[[@LINE+1]]: expected a constraint in impl as declaration, found i32
+  // CHECK:STDERR: COMPILATION ERROR: fail_impl_as_not_constraint.carbon:[[@LINE+1]]: expected a constraint in impl as declaration, found i32
   impl Self as i32;
 }
 
diff --git a/explorer/testdata/interface/fail_impl_as_not_type.carbon b/explorer/testdata/interface/fail_impl_as_not_type.carbon
index c78ca4c9851d..eb7fd399b3e9 100644
--- a/explorer/testdata/interface/fail_impl_as_not_type.carbon
+++ b/explorer/testdata/interface/fail_impl_as_not_type.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 interface A {}
 
 interface B {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_impl_as_not_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
+  // CHECK:STDERR: COMPILATION ERROR: fail_impl_as_not_type.carbon:[[@LINE+1]]: type error in type expression: 'i32' is not implicitly convertible to 'type'
   impl 5 as A;
 }
 
diff --git a/explorer/testdata/interface/fail_impl_bad_member.carbon b/explorer/testdata/interface/fail_impl_bad_member.carbon
index c58765e03ef9..a529b571311c 100644
--- a/explorer/testdata/interface/fail_impl_bad_member.carbon
+++ b/explorer/testdata/interface/fail_impl_bad_member.carbon
@@ -20,7 +20,7 @@ class Point {
     }
     fn Scale[self: Point](v: i32) -> i32 {
       return 0;
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_impl_bad_member.carbon:[[@LINE+3]]: type error in member of implementation
+    // CHECK:STDERR: COMPILATION ERROR: fail_impl_bad_member.carbon:[[@LINE+3]]: type error in member of implementation
     // CHECK:STDERR: expected: fn (i32,) -> class Point
     // CHECK:STDERR: 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 1f652b52b3af..f0d79cc2e792 100644
--- a/explorer/testdata/interface/fail_impl_missing_member.carbon
+++ b/explorer/testdata/interface/fail_impl_missing_member.carbon
@@ -18,7 +18,7 @@ class Point {
     fn Add[self: Point](b: Point) -> Point {
       return {.x = self.x + b.x, .y = self.y + b.y};
     }
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_impl_missing_member.carbon:[[@LINE+1]]: implementation missing Scale
+  // CHECK:STDERR: COMPILATION ERROR: 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 dcbb86b72f71..05a845a4a420 100644
--- a/explorer/testdata/interface/fail_impl_not_type.carbon
+++ b/explorer/testdata/interface/fail_impl_not_type.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 interface Vector {
   fn Zero() -> i32;
 }
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_impl_not_type.carbon:[[@LINE+1]]: type error in type expression: 'String' is not implicitly convertible to 'type'
+// CHECK:STDERR: COMPILATION ERROR: fail_impl_not_type.carbon:[[@LINE+1]]: type error in type expression: 'String' is not implicitly convertible to 'type'
 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 da6a2ece03a1..248eb3374ffb 100644
--- a/explorer/testdata/interface/fail_interface_missing_member.carbon
+++ b/explorer/testdata/interface/fail_interface_missing_member.carbon
@@ -11,7 +11,7 @@ interface Vector {
 }
 
 fn ScaleGeneric[T:! Vector](a: T, s: i32) -> T {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_interface_missing_member.carbon:[[@LINE+1]]: member access, Scale not in interface Vector where T impls interface Vector
+  // CHECK:STDERR: COMPILATION ERROR: fail_interface_missing_member.carbon:[[@LINE+1]]: member access, Scale not in interface Vector where T impls interface Vector
   return a.Scale(s);
 }
 
diff --git a/explorer/testdata/interface/fail_member_lookup_in_definition.carbon b/explorer/testdata/interface/fail_member_lookup_in_definition.carbon
index 6cc240a680c6..00f7ee4e612c 100644
--- a/explorer/testdata/interface/fail_member_lookup_in_definition.carbon
+++ b/explorer/testdata/interface/fail_member_lookup_in_definition.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 interface Vector {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_member_lookup_in_definition.carbon:[[@LINE+1]]: incomplete type `interface Vector` used in member access
+  // CHECK:STDERR: COMPILATION ERROR: fail_member_lookup_in_definition.carbon:[[@LINE+1]]: incomplete type `interface Vector` used in member access
   fn ScalarZero() -> Vector.ScalarType;
   let ScalarType:! type;
 }
diff --git a/explorer/testdata/interface/fail_no_impl.carbon b/explorer/testdata/interface/fail_no_impl.carbon
index 5ecb5df3837c..d4749015cd02 100644
--- a/explorer/testdata/interface/fail_no_impl.carbon
+++ b/explorer/testdata/interface/fail_no_impl.carbon
@@ -23,7 +23,7 @@ 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:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_no_impl.carbon:[[@LINE+1]]: could not find implementation of interface Vector for class Point
+  // CHECK:STDERR: COMPILATION ERROR: 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_qualified_method.carbon b/explorer/testdata/interface/fail_qualified_method.carbon
index cc49d49155e9..186f5ea4a124 100644
--- a/explorer/testdata/interface/fail_qualified_method.carbon
+++ b/explorer/testdata/interface/fail_qualified_method.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 interface Vector {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_qualified_method.carbon:[[@LINE+1]]: qualified declaration names are not permitted in this context
+  // CHECK:STDERR: COMPILATION ERROR: fail_qualified_method.carbon:[[@LINE+1]]: qualified declaration names are not permitted in this context
   fn Vector.Zero() -> i32;
 }
 
diff --git a/explorer/testdata/interface/fail_self_lookup_in_definition.carbon b/explorer/testdata/interface/fail_self_lookup_in_definition.carbon
index a03332a77ac7..e8c1539518b5 100644
--- a/explorer/testdata/interface/fail_self_lookup_in_definition.carbon
+++ b/explorer/testdata/interface/fail_self_lookup_in_definition.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 interface Vector {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_self_lookup_in_definition.carbon:[[@LINE+1]]: incomplete type `interface Vector` used in member access
+  // CHECK:STDERR: COMPILATION ERROR: fail_self_lookup_in_definition.carbon:[[@LINE+1]]: incomplete type `interface Vector` used in member access
   fn ScalarZero() -> Self.ScalarType;
   let ScalarType:! type;
 }
diff --git a/explorer/testdata/interface/fail_use_assoc_const_before_decl.carbon b/explorer/testdata/interface/fail_use_assoc_const_before_decl.carbon
index 6a4a48154845..2f88e4cd4f83 100644
--- a/explorer/testdata/interface/fail_use_assoc_const_before_decl.carbon
+++ b/explorer/testdata/interface/fail_use_assoc_const_before_decl.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 interface IFace {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_use_assoc_const_before_decl.carbon:[[@LINE+1]]: 'C' has not been declared yet
+  // CHECK:STDERR: COMPILATION ERROR: fail_use_assoc_const_before_decl.carbon:[[@LINE+1]]: 'C' has not been declared yet
   let B:! C;
   let C:! IFace;
 }
diff --git a/explorer/testdata/interface/fail_use_assoc_const_in_defn.carbon b/explorer/testdata/interface/fail_use_assoc_const_in_defn.carbon
index 6bb17628a6bb..bdd6fa95015b 100644
--- a/explorer/testdata/interface/fail_use_assoc_const_in_defn.carbon
+++ b/explorer/testdata/interface/fail_use_assoc_const_in_defn.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 interface IFace {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_use_assoc_const_in_defn.carbon:[[@LINE+1]]: 'T' is not usable until after it has been completely declared
+  // CHECK:STDERR: COMPILATION ERROR: fail_use_assoc_const_in_defn.carbon:[[@LINE+1]]: 'T' is not usable until after it has been completely declared
   let T:! T.IFace;
 }
 
diff --git a/explorer/testdata/interface/fail_use_symbolic_member.carbon b/explorer/testdata/interface/fail_use_symbolic_member.carbon
index 96654bf9ffcf..8423f280ab19 100644
--- a/explorer/testdata/interface/fail_use_symbolic_member.carbon
+++ b/explorer/testdata/interface/fail_use_symbolic_member.carbon
@@ -10,7 +10,7 @@ interface X {
   fn F() -> type;
 }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/interface/fail_use_symbolic_member.carbon:[[@LINE+1]]: member lookup for F in symbolic witness 0 of witness for T:! X
+// CHECK:STDERR: COMPILATION ERROR: fail_use_symbolic_member.carbon:[[@LINE+1]]: member lookup for F in symbolic witness 0 of witness for T:! X
 fn G[T:! X]() -> T.F() {
   return {};
 }
diff --git a/explorer/testdata/let/fail_function_args.carbon b/explorer/testdata/let/fail_function_args.carbon
index 9133062b5138..5b28c8a4c58e 100644
--- a/explorer/testdata/let/fail_function_args.carbon
+++ b/explorer/testdata/let/fail_function_args.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn f((var x: i32, y: i32)) -> i32 {
   x = 0;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/let/fail_function_args.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `y`
+  // CHECK:STDERR: COMPILATION ERROR: fail_function_args.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `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 fc8ebed7add1..350790b8fc0b 100644
--- a/explorer/testdata/let/fail_global_assign.carbon
+++ b/explorer/testdata/let/fail_global_assign.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 let x: i32 = 10;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/let/fail_global_assign.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `x`
+  // CHECK:STDERR: COMPILATION ERROR: fail_global_assign.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `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 5349e72a9630..03c73f8de907 100644
--- a/explorer/testdata/let/fail_global_named_self.carbon
+++ b/explorer/testdata/let/fail_global_named_self.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 // Error: Can't use keyword `Self` as the name of a global.
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/let/fail_global_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
+// CHECK:STDERR: SYNTAX ERROR: 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 a1425781443e..a385e1fd9848 100644
--- a/explorer/testdata/let/fail_local_assign.carbon
+++ b/explorer/testdata/let/fail_local_assign.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   let x: auto = 10;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/let/fail_local_assign.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `x`
+  // CHECK:STDERR: COMPILATION ERROR: fail_local_assign.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `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 01a4e6c5d4e9..4810e4187c67 100644
--- a/explorer/testdata/let/fail_local_named_self.carbon
+++ b/explorer/testdata/let/fail_local_named_self.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   // Error: Can't use keyword `Self` as the name of a local.
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/let/fail_local_named_self.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting EQUAL
+  // CHECK:STDERR: SYNTAX ERROR: fail_local_named_self.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting EQUAL
   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 85bfd60e8381..8d7b3cf3c0e5 100644
--- a/explorer/testdata/let/fail_match_choice.carbon
+++ b/explorer/testdata/let/fail_match_choice.carbon
@@ -23,7 +23,7 @@ fn Main() -> i32 {
       n = n - 1;
     }
     case Ints.Two(x: auto, y: auto) => {
-      // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/let/fail_match_choice.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `x`
+      // CHECK:STDERR: COMPILATION ERROR: fail_match_choice.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `x`
       x = 0;
     }
   }
diff --git a/explorer/testdata/let/fail_method_args.carbon b/explorer/testdata/let/fail_method_args.carbon
index 0e5956002030..374930240aa5 100644
--- a/explorer/testdata/let/fail_method_args.carbon
+++ b/explorer/testdata/let/fail_method_args.carbon
@@ -12,7 +12,7 @@ class Point {
   }
 
   fn SetX[self: Point](x: i32) {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/let/fail_method_args.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `x`
+    // CHECK:STDERR: COMPILATION ERROR: fail_method_args.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `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 7e1465b993a2..2a60718f9460 100644
--- a/explorer/testdata/let/fail_tuple_pattern_let_context.carbon
+++ b/explorer/testdata/let/fail_tuple_pattern_let_context.carbon
@@ -10,7 +10,7 @@ fn Main() -> i32 {
   let (var a: auto, b: auto, c: auto, d: auto) = (1, 2, 3, 4);
   a = 0;
   // should fail
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/let/fail_tuple_pattern_let_context.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `c`
+  // CHECK:STDERR: COMPILATION ERROR: fail_tuple_pattern_let_context.carbon:[[@LINE+1]]: Only a reference expression can be assigned to, but got `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 57de6efa7363..a76f963519d3 100644
--- a/explorer/testdata/let/fail_tuple_pattern_let_context_nested.carbon
+++ b/explorer/testdata/let/fail_tuple_pattern_let_context_nested.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/let/fail_tuple_pattern_let_context_nested.carbon:[[@LINE+1]]: syntax error, unexpected LET
+  // CHECK:STDERR: SYNTAX ERROR: 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 e40f2ead0ce1..9b04df9f42b9 100644
--- a/explorer/testdata/let/fail_tuple_pattern_let_in_var.carbon
+++ b/explorer/testdata/let/fail_tuple_pattern_let_in_var.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/let/fail_tuple_pattern_let_in_var.carbon:[[@LINE+1]]: syntax error, unexpected LET
+  // CHECK:STDERR: SYNTAX ERROR: 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/match/fail_exhaustive_exponential_9x.carbon b/explorer/testdata/match/fail_exhaustive_exponential_9x.carbon
index 787b87770e66..0b23fb5b73b9 100644
--- a/explorer/testdata/match/fail_exhaustive_exponential_9x.carbon
+++ b/explorer/testdata/match/fail_exhaustive_exponential_9x.carbon
@@ -27,5 +27,5 @@ 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:STDERR: 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:STDERR: COMPILATION ERROR: 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 8faabfe4c0fc..5cffe47f0b68 100644
--- a/explorer/testdata/match/fail_exhaustive_exponential_series_t.carbon
+++ b/explorer/testdata/match/fail_exhaustive_exponential_series_t.carbon
@@ -36,5 +36,5 @@ 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:STDERR: 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:STDERR: COMPILATION ERROR: 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 344e53216b2c..38ed0daba0d0 100644
--- a/explorer/testdata/match/fail_exhaustive_int.carbon
+++ b/explorer/testdata/match/fail_exhaustive_int.carbon
@@ -11,7 +11,7 @@ fn A(n: i32) -> i32 {
     case 1 => { return 1; }
     case 2 => { return 2; }
   }
-// CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 22794c0574be..9afe8750c1a5 100644
--- a/explorer/testdata/match/fail_not_alternative.carbon
+++ b/explorer/testdata/match/fail_not_alternative.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: i32 = 0;
   match (x) {
-    // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/match/fail_not_alternative.carbon:[[@LINE+1]]: Alternative pattern must have the form of a field access.
+    // CHECK:STDERR: SYNTAX ERROR: 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 9bffaab8f7d5..1490518bfc02 100644
--- a/explorer/testdata/match/fail_not_exhaustive.carbon
+++ b/explorer/testdata/match/fail_not_exhaustive.carbon
@@ -16,7 +16,7 @@ fn A(a: Opt, b: Opt) -> i32 {
     case (Opt.Some(n: i32), _: auto) => { return n; }
     case (_: auto, Opt.Some(n: i32)) => { return n; }
   }
-// CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 bf8f915905be..f1db492d1271 100644
--- a/explorer/testdata/match/fail_not_reachable.carbon
+++ b/explorer/testdata/match/fail_not_reachable.carbon
@@ -15,7 +15,7 @@ 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:STDERR: 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:STDERR: COMPILATION ERROR: 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 b9026ccf2570..7a49b9bd5bb5 100644
--- a/explorer/testdata/match/fail_not_reachable_default.carbon
+++ b/explorer/testdata/match/fail_not_reachable_default.carbon
@@ -16,7 +16,7 @@ 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:STDERR: 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:STDERR: COMPILATION ERROR: 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 0d4d5024a124..27b84bfc2af5 100644
--- a/explorer/testdata/match/fail_pattern_type_mismatch.carbon
+++ b/explorer/testdata/match/fail_pattern_type_mismatch.carbon
@@ -19,7 +19,7 @@ fn Main() -> i32 {
   // expression when checking each pattern.
   match ((a, a)) {
     case (0, n: A) => { return 1; }
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/match/fail_pattern_type_mismatch.carbon:[[@LINE+3]]: type error in `match` pattern type
+    // CHECK:STDERR: COMPILATION ERROR: fail_pattern_type_mismatch.carbon:[[@LINE+3]]: type error in `match` pattern type
     // CHECK:STDERR: expected: (i32, class A)
     // CHECK:STDERR: actual: (class A, i32)
     case (n: A, 0) => { return 1; }
diff --git a/explorer/testdata/match/fail_redundant_int.carbon b/explorer/testdata/match/fail_redundant_int.carbon
index caaf62af1975..e81c097e94ea 100644
--- a/explorer/testdata/match/fail_redundant_int.carbon
+++ b/explorer/testdata/match/fail_redundant_int.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn A(n: i32) -> i32 {
   match (n) {
     case 1 => { return 1; }
-    // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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/member_access/fail_qualified_non_member.carbon b/explorer/testdata/member_access/fail_qualified_non_member.carbon
index 18458eb3994a..3042b113de89 100644
--- a/explorer/testdata/member_access/fail_qualified_non_member.carbon
+++ b/explorer/testdata/member_access/fail_qualified_non_member.carbon
@@ -9,7 +9,7 @@ fn F[self: 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:STDERR: 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:STDERR: COMPILATION ERROR: 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 0bab8cb4b7c3..54e4542b3fe1 100644
--- a/explorer/testdata/member_access/fail_vacuous_access.carbon
+++ b/explorer/testdata/member_access/fail_vacuous_access.carbon
@@ -13,6 +13,6 @@ class X {
 }
 fn Main() -> i32 {
   var a: X = {};
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 eda3efb04129..34bf7c601911 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
@@ -12,7 +12,7 @@ class X {
   }
 }
 fn F[T:! A](a: T) -> i32 {
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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/mixin/fail_circular_mixing.carbon b/explorer/testdata/mixin/fail_circular_mixing.carbon
index 72096f74cd92..36079967ae07 100644
--- a/explorer/testdata/mixin/fail_circular_mixing.carbon
+++ b/explorer/testdata/mixin/fail_circular_mixing.carbon
@@ -9,7 +9,7 @@ __mixin M1 {
   fn F1[self: Self](x: Self) -> Self{
      return x;
   }
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/mixin/fail_circular_mixing.carbon:[[@LINE+1]]: 'M3' has not been declared yet
+  // CHECK:STDERR: COMPILATION ERROR: 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 9f300188e8b4..596d1f63d4cc 100644
--- a/explorer/testdata/mixin/fail_field_member_name_clash.carbon
+++ b/explorer/testdata/mixin/fail_field_member_name_clash.carbon
@@ -15,7 +15,7 @@ __mixin M {
 class C {
   let F: i32 = 0;
   __mix M;
-// CHECK:STDERR: 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:[[@LINE-6]]) 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:[[@LINE-2]])
+// CHECK:STDERR: COMPILATION ERROR: fail_field_member_name_clash.carbon:[[@LINE+1]]: Member named F (declared at fail_field_member_name_clash.carbon:[[@LINE-6]]) cannot be mixed into C because it clashes with an existing member with the same name (declared at fail_field_member_name_clash.carbon:[[@LINE-2]])
 }
 
 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 cbb0c2454561..4b61617ce0cf 100644
--- a/explorer/testdata/mixin/fail_method_member_name_clash.carbon
+++ b/explorer/testdata/mixin/fail_method_member_name_clash.carbon
@@ -17,7 +17,7 @@ class C {
      return x;
   }
   __mix M;
-// CHECK:STDERR: 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:[[@LINE-8]]) 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:[[@LINE-2]])
+// CHECK:STDERR: COMPILATION ERROR: fail_method_member_name_clash.carbon:[[@LINE+1]]: Member named F (declared at fail_method_member_name_clash.carbon:[[@LINE-8]]) cannot be mixed into C because it clashes with an existing member with the same name (declared at fail_method_member_name_clash.carbon:[[@LINE-2]])
 }
 
 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 171b85f12ece..e8700120e2aa 100644
--- a/explorer/testdata/mixin/fail_mix_as_type_expr.carbon
+++ b/explorer/testdata/mixin/fail_mix_as_type_expr.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 __mixin Operations {}
 
 fn Main() -> i32 {
-   // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/mixin/fail_mix_as_type_expr.carbon:[[@LINE+1]]: invalid use of mixin Operations
+   // CHECK:STDERR: COMPILATION ERROR: fail_mix_as_type_expr.carbon:[[@LINE+1]]: invalid use of 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 a1c13c8ff586..d39f48f57263 100644
--- a/explorer/testdata/mixin/fail_mix_diamond_clash.carbon
+++ b/explorer/testdata/mixin/fail_mix_diamond_clash.carbon
@@ -26,7 +26,7 @@ __mixin M3 {
 class C {
   __mix M2;
   __mix M3;
-// CHECK:STDERR: 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:[[@LINE-18]]) is being mixed multiple times into C
+// CHECK:STDERR: COMPILATION ERROR: fail_mix_diamond_clash.carbon:[[@LINE+1]]: Member named F1 (declared at fail_mix_diamond_clash.carbon:[[@LINE-18]]) 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 2f56afbe9fd5..09d4423671fd 100644
--- a/explorer/testdata/mixin/fail_mix_in_global.carbon
+++ b/explorer/testdata/mixin/fail_mix_in_global.carbon
@@ -12,7 +12,7 @@ __mixin Operations {
   }
 }
 
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/mixin/fail_mix_in_global.carbon:[[@LINE+1]]: syntax error, unexpected MIX, expecting END_OF_FILE
+// CHECK:STDERR: SYNTAX ERROR: 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 a4089482cf27..5dc774dd7d89 100644
--- a/explorer/testdata/mixin/fail_mix_in_impl.carbon
+++ b/explorer/testdata/mixin/fail_mix_in_impl.carbon
@@ -17,7 +17,7 @@ interface A {
 }
 
 external impl i32 as A {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/mixin/fail_mix_in_impl.carbon:[[@LINE+1]]: syntax error, unexpected MIX
+  // CHECK:STDERR: SYNTAX ERROR: fail_mix_in_impl.carbon:[[@LINE+1]]: syntax error, unexpected MIX
   __mix Operations;
   fn F() {}
 }
diff --git a/explorer/testdata/mixin/fail_mix_invalid.carbon b/explorer/testdata/mixin/fail_mix_invalid.carbon
index 0474f2b76363..31cc4010a522 100644
--- a/explorer/testdata/mixin/fail_mix_invalid.carbon
+++ b/explorer/testdata/mixin/fail_mix_invalid.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 __mixin Mixin {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/mixin/fail_mix_invalid.carbon:[[@LINE+1]]: Not a valid mixin: `()`
+  // CHECK:STDERR: COMPILATION ERROR: fail_mix_invalid.carbon:[[@LINE+1]]: Not a valid mixin: `()`
   __mix ();
 }
 
diff --git a/explorer/testdata/mixin/fail_mix_invalid_array.carbon b/explorer/testdata/mixin/fail_mix_invalid_array.carbon
index a7188f28fe47..e1e2881f9d71 100644
--- a/explorer/testdata/mixin/fail_mix_invalid_array.carbon
+++ b/explorer/testdata/mixin/fail_mix_invalid_array.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 class C {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/mixin/fail_mix_invalid_array.carbon:[[@LINE+1]]: type error in type expression: 'bool' is not implicitly convertible to 'type'
+  // CHECK:STDERR: COMPILATION ERROR: fail_mix_invalid_array.carbon:[[@LINE+1]]: type error in type expression: 'bool' is not implicitly convertible to 'type'
   __mix [true; true];
 }
 
diff --git a/explorer/testdata/mixin/fail_mix_members_clash.carbon b/explorer/testdata/mixin/fail_mix_members_clash.carbon
index 365fe15169ad..16149598baa2 100644
--- a/explorer/testdata/mixin/fail_mix_members_clash.carbon
+++ b/explorer/testdata/mixin/fail_mix_members_clash.carbon
@@ -19,7 +19,7 @@ __mixin M2 {
 class C {
   __mix M1;
   __mix M2;
-// CHECK:STDERR: 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:[[@LINE-6]]) 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:[[@LINE-11]])
+// CHECK:STDERR: COMPILATION ERROR: fail_mix_members_clash.carbon:[[@LINE+1]]: Member named F1 (declared at fail_mix_members_clash.carbon:[[@LINE-6]]) cannot be mixed into C because it clashes with an existing member with the same name (declared at fail_mix_members_clash.carbon:[[@LINE-11]])
 }
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/mixin/fail_qualified_method.carbon b/explorer/testdata/mixin/fail_qualified_method.carbon
index 5f620f363b24..7a367178cbd7 100644
--- a/explorer/testdata/mixin/fail_qualified_method.carbon
+++ b/explorer/testdata/mixin/fail_qualified_method.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 __mixin Operations {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/mixin/fail_qualified_method.carbon:[[@LINE+1]]: qualified declaration names are not permitted in this context
+  // CHECK:STDERR: COMPILATION ERROR: fail_qualified_method.carbon:[[@LINE+1]]: qualified declaration names are not permitted in this context
   fn Operations.Square[self: Self](x:i32) -> i32{
     return x * x;
   }
diff --git a/explorer/testdata/mixin/fail_recursive_mixing.carbon b/explorer/testdata/mixin/fail_recursive_mixing.carbon
index 7af3c2f3335b..5d4448e346a0 100644
--- a/explorer/testdata/mixin/fail_recursive_mixing.carbon
+++ b/explorer/testdata/mixin/fail_recursive_mixing.carbon
@@ -9,7 +9,7 @@ __mixin M1 {
   fn F1[self: Self](x: Self) -> Self{
      return x;
   }
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/mixin/fail_recursive_mixing.carbon:[[@LINE+1]]: incomplete mixin `M1` used in mix declaration
+  // CHECK:STDERR: COMPILATION ERROR: fail_recursive_mixing.carbon:[[@LINE+1]]: incomplete mixin `M1` used in mix declaration
   __mix M1;
 }
 
diff --git a/explorer/testdata/mixin/fail_self_substitution.carbon b/explorer/testdata/mixin/fail_self_substitution.carbon
index 9bb637e17007..b6ed781e8e92 100644
--- a/explorer/testdata/mixin/fail_self_substitution.carbon
+++ b/explorer/testdata/mixin/fail_self_substitution.carbon
@@ -34,7 +34,7 @@ class Complex {
 fn Main() -> i32 {
   var p: Point = Point.Origin();
   var c: Complex = {.r = 42, .i = 1};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/mixin/fail_self_substitution.carbon:[[@LINE+1]]: mismatch in non-deduced types, `class Complex` is not implicitly convertible to `class Point`
+  // CHECK:STDERR: COMPILATION ERROR: fail_self_substitution.carbon:[[@LINE+1]]: mismatch in non-deduced types, `class Complex` is not implicitly convertible to `class Point`
   var p1: Point = p.F(c);
 
   return p1.x - 42;
diff --git a/explorer/testdata/name_lookup/fail_block_duplicate.carbon b/explorer/testdata/name_lookup/fail_block_duplicate.carbon
index 1f3af89aff8f..7a568fc9bd92 100644
--- a/explorer/testdata/name_lookup/fail_block_duplicate.carbon
+++ b/explorer/testdata/name_lookup/fail_block_duplicate.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32 = 0;
-  // CHECK:STDERR: 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:[[@LINE-1]]
+  // CHECK:STDERR: COMPILATION ERROR: fail_block_duplicate.carbon:[[@LINE+1]]: Duplicate name `x` also found at fail_block_duplicate.carbon:[[@LINE-1]]
   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 f19dbb4b3999..fc87d221cf61 100644
--- a/explorer/testdata/name_lookup/fail_choice_duplicate.carbon
+++ b/explorer/testdata/name_lookup/fail_choice_duplicate.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 choice Ints {
   None,
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/name_lookup/fail_choice_duplicate.carbon:[[@LINE+1]]: Duplicate name `None` in choice type
+  // CHECK:STDERR: COMPILATION ERROR: 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 5e6c773d4ed2..be5b507d29e8 100644
--- a/explorer/testdata/name_lookup/fail_class_duplicate.carbon
+++ b/explorer/testdata/name_lookup/fail_class_duplicate.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 class Foo {
   var x: i32;
-  // CHECK:STDERR: 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:[[@LINE-1]]
+  // CHECK:STDERR: COMPILATION ERROR: fail_class_duplicate.carbon:[[@LINE+1]]: Duplicate name `x` also found at fail_class_duplicate.carbon:[[@LINE-1]]
   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 910c0d68eb2f..3929f5bb3562 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
@@ -17,7 +17,7 @@ class A {
     return 0;
   }
 
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/name_lookup/fail_class_fn_use_before_declaration.carbon:[[@LINE+1]]: 'I' has not been declared yet
+  // CHECK:STDERR: COMPILATION ERROR: 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 9b5136bb850f..930a435ec786 100644
--- a/explorer/testdata/name_lookup/fail_class_use_in_params.carbon
+++ b/explorer/testdata/name_lookup/fail_class_use_in_params.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 b0a86db3528b..9a90d269adf0 100644
--- a/explorer/testdata/name_lookup/fail_fn_use_in_param.carbon
+++ b/explorer/testdata/name_lookup/fail_fn_use_in_param.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 af2cdde8755d..5b03936e776a 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
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 1ae57094a625..1af7826134c7 100644
--- a/explorer/testdata/name_lookup/fail_global_duplicate.carbon
+++ b/explorer/testdata/name_lookup/fail_global_duplicate.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 var x: i32 = 0;
-// CHECK:STDERR: 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:[[@LINE-1]]
+// CHECK:STDERR: COMPILATION ERROR: fail_global_duplicate.carbon:[[@LINE+1]]: Duplicate name `x` also found at fail_global_duplicate.carbon:[[@LINE-1]]
 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 924ba2aed4aa..9e130cb3ac15 100644
--- a/explorer/testdata/name_lookup/fail_use_before_declare.carbon
+++ b/explorer/testdata/name_lookup/fail_use_before_declare.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/name_lookup/fail_use_before_declare.carbon:[[@LINE+1]]: could not resolve 'x'
+  // CHECK:STDERR: COMPILATION ERROR: 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 c0a5224734a3..f73bc9132ea3 100644
--- a/explorer/testdata/name_lookup/fail_var_use_before_declaration.carbon
+++ b/explorer/testdata/name_lookup/fail_var_use_before_declaration.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 // Test that a global variable may not depend on a later global.
 // Error expected.
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/name_lookup/fail_var_use_before_declaration.carbon:[[@LINE+1]]: 'y' has not been declared yet
+// CHECK:STDERR: COMPILATION ERROR: 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/named_constraint/fail_associated_constant.carbon b/explorer/testdata/named_constraint/fail_associated_constant.carbon
index 8bab7670680d..10bd559201d0 100644
--- a/explorer/testdata/named_constraint/fail_associated_constant.carbon
+++ b/explorer/testdata/named_constraint/fail_associated_constant.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 constraint X {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/named_constraint/fail_associated_constant.carbon:[[@LINE+1]]: associated constant not permitted in named constraint
+  // CHECK:STDERR: COMPILATION ERROR: fail_associated_constant.carbon:[[@LINE+1]]: associated constant not permitted in named constraint
   let N:! type;
 }
 
diff --git a/explorer/testdata/named_constraint/fail_associated_function.carbon b/explorer/testdata/named_constraint/fail_associated_function.carbon
index 4071500355bc..4300c8696644 100644
--- a/explorer/testdata/named_constraint/fail_associated_function.carbon
+++ b/explorer/testdata/named_constraint/fail_associated_function.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 constraint X {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/named_constraint/fail_associated_function.carbon:[[@LINE+1]]: associated function not permitted in named constraint
+  // CHECK:STDERR: COMPILATION ERROR: fail_associated_function.carbon:[[@LINE+1]]: associated function not permitted in named constraint
   fn F();
 }
 
diff --git a/explorer/testdata/named_constraint/fail_compound_member_access.carbon b/explorer/testdata/named_constraint/fail_compound_member_access.carbon
index 43369f9212f3..adebecdbdb8f 100644
--- a/explorer/testdata/named_constraint/fail_compound_member_access.carbon
+++ b/explorer/testdata/named_constraint/fail_compound_member_access.carbon
@@ -25,6 +25,6 @@ fn Main() -> i32 {
   // MemberName value. We will likely need MemberName to remember the
   // constraint as written, not only the interface in which the member was
   // found.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/named_constraint/fail_compound_member_access.carbon:[[@LINE+1]]: could not find implementation of interface MyAddWith(T = Self) for i32
+  // CHECK:STDERR: COMPILATION ERROR: fail_compound_member_access.carbon:[[@LINE+1]]: could not find implementation of interface MyAddWith(T = Self) for i32
   return n.(MyAdd.Op)(n);
 }
diff --git a/explorer/testdata/named_constraint/fail_impl_as_member_access.carbon b/explorer/testdata/named_constraint/fail_impl_as_member_access.carbon
index 3a11c8a36fd9..7149a0cd52a5 100644
--- a/explorer/testdata/named_constraint/fail_impl_as_member_access.carbon
+++ b/explorer/testdata/named_constraint/fail_impl_as_member_access.carbon
@@ -17,7 +17,7 @@ constraint ImplAsHasFoo {
 fn CallFoo[T:! ImplAsHasFoo](x: T) {
   // OK, T is HasFoo.
   x.(HasFoo.Foo)();
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/named_constraint/fail_impl_as_member_access.carbon:[[@LINE+1]]: member access, Foo not in constraint ImplAsHasFoo where T impls interface HasFoo
+  // CHECK:STDERR: COMPILATION ERROR: fail_impl_as_member_access.carbon:[[@LINE+1]]: member access, Foo not in constraint ImplAsHasFoo where T impls interface HasFoo
   x.Foo();
 }
 
diff --git a/explorer/testdata/namespace/fail_members_not_in_outer_scope.carbon b/explorer/testdata/namespace/fail_members_not_in_outer_scope.carbon
index 8c11523b2988..207c1c1b53bf 100644
--- a/explorer/testdata/namespace/fail_members_not_in_outer_scope.carbon
+++ b/explorer/testdata/namespace/fail_members_not_in_outer_scope.carbon
@@ -11,6 +11,6 @@ namespace N;
 fn N.F() -> i32 { return 0; }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/namespace/fail_members_not_in_outer_scope.carbon:[[@LINE+1]]: could not resolve 'F'
+  // CHECK:STDERR: COMPILATION ERROR: fail_members_not_in_outer_scope.carbon:[[@LINE+1]]: could not resolve 'F'
   return F();
 }
diff --git a/explorer/testdata/namespace/fail_missing_nested.carbon b/explorer/testdata/namespace/fail_missing_nested.carbon
index 19e9f04949bc..4ad8f7d5a9f7 100644
--- a/explorer/testdata/namespace/fail_missing_nested.carbon
+++ b/explorer/testdata/namespace/fail_missing_nested.carbon
@@ -10,7 +10,7 @@ namespace A;
 namespace A.B;
 namespace A.B.C;
 fn A.B.C.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/namespace/fail_missing_nested.carbon:[[@LINE+1]]: name 'D' has not been declared in namespace A.B.C
+  // CHECK:STDERR: COMPILATION ERROR: fail_missing_nested.carbon:[[@LINE+1]]: name 'D' has not been declared in namespace A.B.C
   D
   // Don't combine with the previous line. This test is verifying that the
   // diagnostic points at the right token.
diff --git a/explorer/testdata/namespace/fail_qualifier_not_namespace.carbon b/explorer/testdata/namespace/fail_qualifier_not_namespace.carbon
index f2acd0458f74..31427690b9f9 100644
--- a/explorer/testdata/namespace/fail_qualifier_not_namespace.carbon
+++ b/explorer/testdata/namespace/fail_qualifier_not_namespace.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn F() {}
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/namespace/fail_qualifier_not_namespace.carbon:[[@LINE+1]]: fn F cannot be used as a name qualifier
+// CHECK:STDERR: COMPILATION ERROR: fail_qualifier_not_namespace.carbon:[[@LINE+1]]: fn F cannot be used as a name qualifier
 fn F.G() {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/namespace/fail_unknown_member.carbon b/explorer/testdata/namespace/fail_unknown_member.carbon
index 176c6e54e193..87bc85d11d53 100644
--- a/explorer/testdata/namespace/fail_unknown_member.carbon
+++ b/explorer/testdata/namespace/fail_unknown_member.carbon
@@ -9,6 +9,6 @@ package ExplorerTest api;
 namespace N;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/namespace/fail_unknown_member.carbon:[[@LINE+1]]: name 'value' has not been declared in namespace N
+  // CHECK:STDERR: COMPILATION ERROR: fail_unknown_member.carbon:[[@LINE+1]]: name 'value' has not been declared in namespace N
   return N.value;
 }
diff --git a/explorer/testdata/namespace/fail_unknown_namespace.carbon b/explorer/testdata/namespace/fail_unknown_namespace.carbon
index e7fe5aab82c4..c554618d42b3 100644
--- a/explorer/testdata/namespace/fail_unknown_namespace.carbon
+++ b/explorer/testdata/namespace/fail_unknown_namespace.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/namespace/fail_unknown_namespace.carbon:[[@LINE+1]]: name 'N' has not been declared in this scope
+// CHECK:STDERR: COMPILATION ERROR: fail_unknown_namespace.carbon:[[@LINE+1]]: name 'N' has not been declared in this scope
 fn N.F() {}
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/namespace/fail_use_as_expression.carbon b/explorer/testdata/namespace/fail_use_as_expression.carbon
index 9747035a5be4..f07a7bcd3207 100644
--- a/explorer/testdata/namespace/fail_use_as_expression.carbon
+++ b/explorer/testdata/namespace/fail_use_as_expression.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 namespace N;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/namespace/fail_use_as_expression.carbon:[[@LINE+1]]: expected `.member_name` after name of namespace N
+  // CHECK:STDERR: COMPILATION ERROR: fail_use_as_expression.carbon:[[@LINE+1]]: expected `.member_name` after name of namespace N
   N;
   return 0;
 }
diff --git a/explorer/testdata/namespace/fail_use_as_value.carbon b/explorer/testdata/namespace/fail_use_as_value.carbon
index c4a113374d56..b5f0358192e7 100644
--- a/explorer/testdata/namespace/fail_use_as_value.carbon
+++ b/explorer/testdata/namespace/fail_use_as_value.carbon
@@ -11,6 +11,6 @@ namespace N;
 fn F[T:! type](x: T) -> T { return x; }
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/namespace/fail_use_as_value.carbon:[[@LINE+1]]: expected `.member_name` after name of namespace N
+  // CHECK:STDERR: COMPILATION ERROR: fail_use_as_value.carbon:[[@LINE+1]]: expected `.member_name` after name of namespace N
   return F(N);
 }
diff --git a/explorer/testdata/operators/fail_combine_lhs.carbon b/explorer/testdata/operators/fail_combine_lhs.carbon
index d04878a7bf42..26383ad26dda 100644
--- a/explorer/testdata/operators/fail_combine_lhs.carbon
+++ b/explorer/testdata/operators/fail_combine_lhs.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/operators/fail_combine_lhs.carbon:[[@LINE+1]]: expected a constraint in first operand of `&`, found i32
+// CHECK:STDERR: COMPILATION ERROR: fail_combine_lhs.carbon:[[@LINE+1]]: expected a constraint in first operand of `&`, found i32
 fn F[T:! i32 & type]();
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/operators/fail_combine_rhs.carbon b/explorer/testdata/operators/fail_combine_rhs.carbon
index 55eb0cfa84d2..3bb6f24e8f75 100644
--- a/explorer/testdata/operators/fail_combine_rhs.carbon
+++ b/explorer/testdata/operators/fail_combine_rhs.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 class C {}
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/operators/fail_combine_rhs.carbon:[[@LINE+1]]: expected a constraint in second operand of `&`, found class C
+// CHECK:STDERR: COMPILATION ERROR: fail_combine_rhs.carbon:[[@LINE+1]]: expected a constraint in second operand of `&`, found class C
 fn F[T:! type & C]();
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/operators/fail_div_by_zero.carbon b/explorer/testdata/operators/fail_div_by_zero.carbon
index cf609fd6d373..085ce2153955 100644
--- a/explorer/testdata/operators/fail_div_by_zero.carbon
+++ b/explorer/testdata/operators/fail_div_by_zero.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/operators/fail_div_by_zero.carbon:[[@LINE+1]]: division by zero
+  // CHECK:STDERR: RUNTIME ERROR: fail_div_by_zero.carbon:[[@LINE+1]]: division by zero
   var a: auto = 5 / 0;
   return 0;
 }
diff --git a/explorer/testdata/operators/fail_left_shift_large_rhs.carbon b/explorer/testdata/operators/fail_left_shift_large_rhs.carbon
index 4a28d73e9c9e..86ed85194971 100644
--- a/explorer/testdata/operators/fail_left_shift_large_rhs.carbon
+++ b/explorer/testdata/operators/fail_left_shift_large_rhs.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: Integer overflow
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: Integer overflow
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/fail_left_shift_negative_rhs.carbon b/explorer/testdata/operators/fail_left_shift_negative_rhs.carbon
index dcec9156f527..a633e90577ac 100644
--- a/explorer/testdata/operators/fail_left_shift_negative_rhs.carbon
+++ b/explorer/testdata/operators/fail_left_shift_negative_rhs.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: Integer overflow
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: Integer overflow
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/fail_mod_by_zero.carbon b/explorer/testdata/operators/fail_mod_by_zero.carbon
index 50b950a35317..17590b9c9364 100644
--- a/explorer/testdata/operators/fail_mod_by_zero.carbon
+++ b/explorer/testdata/operators/fail_mod_by_zero.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/operators/fail_mod_by_zero.carbon:[[@LINE+1]]: division by zero
+  // CHECK:STDERR: RUNTIME ERROR: fail_mod_by_zero.carbon:[[@LINE+1]]: division by zero
   var a: auto = 5 % 0;
   return 0;
 }
diff --git a/explorer/testdata/operators/fail_no_add.carbon b/explorer/testdata/operators/fail_no_add.carbon
index f6f4534972fd..cd69ae56895b 100644
--- a/explorer/testdata/operators/fail_no_add.carbon
+++ b/explorer/testdata/operators/fail_no_add.carbon
@@ -10,7 +10,7 @@ class A {}
 
 fn Main() -> i32 {
   var a: A = {};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/operators/fail_no_add.carbon:[[@LINE+2]]: type error in `+`:
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_add.carbon:[[@LINE+2]]: type error in `+`:
   // CHECK:STDERR: 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 b73d59b8c88f..07bf1c3ae6ce 100644
--- a/explorer/testdata/operators/fail_no_mul.carbon
+++ b/explorer/testdata/operators/fail_no_mul.carbon
@@ -10,7 +10,7 @@ class A {}
 
 fn Main() -> i32 {
   var a: A = {};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/operators/fail_no_mul.carbon:[[@LINE+2]]: type error in `*`:
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_mul.carbon:[[@LINE+2]]: type error in `*`:
   // CHECK:STDERR: 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 7242fbfc99a8..bb4128a86570 100644
--- a/explorer/testdata/operators/fail_no_negate.carbon
+++ b/explorer/testdata/operators/fail_no_negate.carbon
@@ -10,7 +10,7 @@ class A {}
 
 fn Main() -> i32 {
   var a: A = {};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/operators/fail_no_negate.carbon:[[@LINE+2]]: type error in `-`:
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_negate.carbon:[[@LINE+2]]: type error in `-`:
   // CHECK:STDERR: 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 4aa503e380b3..30af043f12e7 100644
--- a/explorer/testdata/operators/fail_no_sub.carbon
+++ b/explorer/testdata/operators/fail_no_sub.carbon
@@ -10,7 +10,7 @@ class A {}
 
 fn Main() -> i32 {
   var a: A = {};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/operators/fail_no_sub.carbon:[[@LINE+2]]: type error in `-`:
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_sub.carbon:[[@LINE+2]]: type error in `-`:
   // CHECK:STDERR: could not find implementation of interface SubWith(U = i32) for class A
   a - 1;
   return 0;
diff --git a/explorer/testdata/operators/fail_overflow_add.carbon b/explorer/testdata/operators/fail_overflow_add.carbon
index b4b2a781273a..9c41ed48b655 100644
--- a/explorer/testdata/operators/fail_overflow_add.carbon
+++ b/explorer/testdata/operators/fail_overflow_add.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/operators/fail_overflow_add.carbon:[[@LINE+1]]: integer overflow
+  // CHECK:STDERR: RUNTIME ERROR: fail_overflow_add.carbon:[[@LINE+1]]: integer overflow
   var a: auto = 2147483647 + 1;
   return 0;
 }
diff --git a/explorer/testdata/operators/fail_overflow_div.carbon b/explorer/testdata/operators/fail_overflow_div.carbon
index eb85868a6bc7..a5c9fcdb3108 100644
--- a/explorer/testdata/operators/fail_overflow_div.carbon
+++ b/explorer/testdata/operators/fail_overflow_div.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/operators/fail_overflow_div.carbon:[[@LINE+1]]: integer overflow
+  // CHECK:STDERR: RUNTIME ERROR: fail_overflow_div.carbon:[[@LINE+1]]: integer overflow
   var a: auto = (-2147483647 -1) /-1;
   return 0;
 }
diff --git a/explorer/testdata/operators/fail_overflow_multiply.carbon b/explorer/testdata/operators/fail_overflow_multiply.carbon
index 048d47ea0b08..4bac78fe11bf 100644
--- a/explorer/testdata/operators/fail_overflow_multiply.carbon
+++ b/explorer/testdata/operators/fail_overflow_multiply.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/operators/fail_overflow_multiply.carbon:[[@LINE+1]]: integer overflow
+  // CHECK:STDERR: RUNTIME ERROR: fail_overflow_multiply.carbon:[[@LINE+1]]: integer overflow
   var a: auto = 1000000000 * 1000000000;
   return 0;
 }
diff --git a/explorer/testdata/operators/fail_overflow_sub.carbon b/explorer/testdata/operators/fail_overflow_sub.carbon
index 32b239601c39..edec1b75438f 100644
--- a/explorer/testdata/operators/fail_overflow_sub.carbon
+++ b/explorer/testdata/operators/fail_overflow_sub.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/operators/fail_overflow_sub.carbon:[[@LINE+1]]: integer overflow
+  // CHECK:STDERR: RUNTIME ERROR: fail_overflow_sub.carbon:[[@LINE+1]]: integer overflow
   var a: auto = -2147483647 - 2;
   return 0;
 }
diff --git a/explorer/testdata/operators/fail_right_shift_large_rhs.carbon b/explorer/testdata/operators/fail_right_shift_large_rhs.carbon
index d242c876f13f..22bb572a3b58 100644
--- a/explorer/testdata/operators/fail_right_shift_large_rhs.carbon
+++ b/explorer/testdata/operators/fail_right_shift_large_rhs.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: Integer overflow
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: Integer overflow
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/operators/fail_right_shift_negative_rhs.carbon b/explorer/testdata/operators/fail_right_shift_negative_rhs.carbon
index 47311f506985..c0a99e5d691c 100644
--- a/explorer/testdata/operators/fail_right_shift_negative_rhs.carbon
+++ b/explorer/testdata/operators/fail_right_shift_negative_rhs.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: Integer overflow
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: Integer overflow
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/optional/fail_optional_get_empty.carbon b/explorer/testdata/optional/fail_optional_get_empty.carbon
index aa9e70b01997..f1aab77d6144 100644
--- a/explorer/testdata/optional/fail_optional_get_empty.carbon
+++ b/explorer/testdata/optional/fail_optional_get_empty.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: "Attempted to unwrap empty Optional"
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: "Attempted to unwrap empty Optional"
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/package/fail_missing.carbon b/explorer/testdata/package/fail_missing.carbon
index 50dddd3ecaf5..93194c039a67 100644
--- a/explorer/testdata/package/fail_missing.carbon
+++ b/explorer/testdata/package/fail_missing.carbon
@@ -4,7 +4,7 @@
 //
 // AUTOUPDATE
 
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/package/fail_missing.carbon:[[@LINE+1]]: syntax error, unexpected FN, expecting PACKAGE
+// CHECK:STDERR: SYNTAX ERROR: fail_missing.carbon:[[@LINE+1]]: syntax error, unexpected FN, expecting PACKAGE
 fn Main() -> i32 {
   return 0;
 }
diff --git a/explorer/testdata/pointer/fail_delete_uninit.carbon b/explorer/testdata/pointer/fail_delete_uninit.carbon
index cc6b4944ab08..212279ecadaa 100644
--- a/explorer/testdata/pointer/fail_delete_uninit.carbon
+++ b/explorer/testdata/pointer/fail_delete_uninit.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var p: i32*;
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/pointer/fail_delete_uninit.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<p>>
+  // CHECK:STDERR: RUNTIME ERROR: fail_delete_uninit.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<p>>
   heap.Delete(p);
   return 0;
 }
diff --git a/explorer/testdata/pointer/fail_intrinsic_delete_no_args.carbon b/explorer/testdata/pointer/fail_intrinsic_delete_no_args.carbon
index c4d13a74f8ed..a003a1ba96f8 100644
--- a/explorer/testdata/pointer/fail_intrinsic_delete_no_args.carbon
+++ b/explorer/testdata/pointer/fail_intrinsic_delete_no_args.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/pointer/fail_intrinsic_delete_no_args.carbon:[[@LINE+1]]: __intrinsic_delete takes 1 argument
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_delete_no_args.carbon:[[@LINE+1]]: __intrinsic_delete takes 1 argument
   __intrinsic_delete();
   return 0;
 }
diff --git a/explorer/testdata/pointer/fail_intrinsic_delete_type.carbon b/explorer/testdata/pointer/fail_intrinsic_delete_type.carbon
index 4c6229de1475..f97d17a3792a 100644
--- a/explorer/testdata/pointer/fail_intrinsic_delete_type.carbon
+++ b/explorer/testdata/pointer/fail_intrinsic_delete_type.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/pointer/fail_intrinsic_delete_type.carbon:[[@LINE+3]]: type error in *
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_delete_type.carbon:[[@LINE+3]]: type error in *
   // CHECK:STDERR: expected a pointer type
   // CHECK:STDERR: actual: i32
   __intrinsic_delete(x);
diff --git a/explorer/testdata/pointer/fail_intrinsic_new_no_args.carbon b/explorer/testdata/pointer/fail_intrinsic_new_no_args.carbon
index c54c20af9119..f1c348ebb732 100644
--- a/explorer/testdata/pointer/fail_intrinsic_new_no_args.carbon
+++ b/explorer/testdata/pointer/fail_intrinsic_new_no_args.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/pointer/fail_intrinsic_new_no_args.carbon:[[@LINE+1]]: __intrinsic_new takes 1 argument
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_new_no_args.carbon:[[@LINE+1]]: __intrinsic_new takes 1 argument
   __intrinsic_new();
   return 0;
 }
diff --git a/explorer/testdata/pointer/fail_invalid_ptr_conversion1.carbon b/explorer/testdata/pointer/fail_invalid_ptr_conversion1.carbon
index 97b85fc534ee..bd016a6746ea 100644
--- a/explorer/testdata/pointer/fail_invalid_ptr_conversion1.carbon
+++ b/explorer/testdata/pointer/fail_invalid_ptr_conversion1.carbon
@@ -11,7 +11,7 @@ class A {}
 fn Main() -> i32 {
   var a: A = {};
   var b: A* = &a;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/pointer/fail_invalid_ptr_conversion1.carbon:[[@LINE+1]]: type error in initializer of variable: 'class A*' is not implicitly convertible to 'i32'
+  // CHECK:STDERR: COMPILATION ERROR: fail_invalid_ptr_conversion1.carbon:[[@LINE+1]]: type error in initializer of variable: 'class A*' is not implicitly convertible to 'i32'
   var c: i32 = b;
   return 1;
 }
diff --git a/explorer/testdata/pointer/fail_invalid_ptr_conversion2.carbon b/explorer/testdata/pointer/fail_invalid_ptr_conversion2.carbon
index 0bf3d9dfebaf..924432252950 100644
--- a/explorer/testdata/pointer/fail_invalid_ptr_conversion2.carbon
+++ b/explorer/testdata/pointer/fail_invalid_ptr_conversion2.carbon
@@ -11,7 +11,7 @@ class A {}
 fn Main() -> i32 {
   var a: i32 = 0;
   var b: i32* = &a;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/pointer/fail_invalid_ptr_conversion2.carbon:[[@LINE+1]]: type error in initializer of variable: 'i32*' is not implicitly convertible to 'class A*'
+  // CHECK:STDERR: COMPILATION ERROR: fail_invalid_ptr_conversion2.carbon:[[@LINE+1]]: type error in initializer of variable: 'i32*' is not implicitly convertible to 'class A*'
   var c: A* = b;
   return 1;
 }
diff --git a/explorer/testdata/pointer/fail_rvalue_addressof.carbon b/explorer/testdata/pointer/fail_rvalue_addressof.carbon
index 1e53da57e24f..01cf1f27bc25 100644
--- a/explorer/testdata/pointer/fail_rvalue_addressof.carbon
+++ b/explorer/testdata/pointer/fail_rvalue_addressof.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32 = 5;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/pointer/fail_rvalue_addressof.carbon:[[@LINE+1]]: Argument to & should be a reference expression.
+  // CHECK:STDERR: COMPILATION ERROR: fail_rvalue_addressof.carbon:[[@LINE+1]]: Argument to & should be a reference expression.
   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 308d18bf6a3e..9ccc23fd6a2e 100644
--- a/explorer/testdata/pointer/fail_use_after_free.carbon
+++ b/explorer/testdata/pointer/fail_use_after_free.carbon
@@ -9,6 +9,6 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var p: i32* = heap.New(5);
   heap.Delete(p);
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/pointer/fail_use_after_free.carbon:[[@LINE+1]]: undefined behavior: access to dead value 5
+  // CHECK:STDERR: RUNTIME ERROR: fail_use_after_free.carbon:[[@LINE+1]]: undefined behavior: access to dead value 5
   return *p;
 }
diff --git a/explorer/testdata/print/fail_index_bounds0.carbon b/explorer/testdata/print/fail_index_bounds0.carbon
index 1d7702d78807..a332420270a7 100644
--- a/explorer/testdata/print/fail_index_bounds0.carbon
+++ b/explorer/testdata/print/fail_index_bounds0.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/print/fail_index_bounds0.carbon:[[@LINE+1]]: Index invalid with argument count of 0 at offset 8 in `Print: {0}`
+  // CHECK:STDERR: RUNTIME ERROR: fail_index_bounds0.carbon:[[@LINE+1]]: Index invalid with argument count of 0 at offset 8 in `Print: {0}`
   Print("Print: {0}");
   return 0;
 }
diff --git a/explorer/testdata/print/fail_index_bounds1.carbon b/explorer/testdata/print/fail_index_bounds1.carbon
index 3eaab7f83c62..73dea8d9b58d 100644
--- a/explorer/testdata/print/fail_index_bounds1.carbon
+++ b/explorer/testdata/print/fail_index_bounds1.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/print/fail_index_bounds1.carbon:[[@LINE+1]]: Index invalid with argument count of 1 at offset 12 in `Print: {0} {1}`
+  // CHECK:STDERR: RUNTIME ERROR: fail_index_bounds1.carbon:[[@LINE+1]]: Index invalid with argument count of 1 at offset 12 in `Print: {0} {1}`
   Print("Print: {0} {1}", 1);
   return 0;
 }
diff --git a/explorer/testdata/print/fail_index_empty.carbon b/explorer/testdata/print/fail_index_empty.carbon
index 2bc565f3f5b1..13be68480348 100644
--- a/explorer/testdata/print/fail_index_empty.carbon
+++ b/explorer/testdata/print/fail_index_empty.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/print/fail_index_empty.carbon:[[@LINE+1]]: Invalid `{}` in `Print: {}`
+  // CHECK:STDERR: RUNTIME ERROR: fail_index_empty.carbon:[[@LINE+1]]: Invalid `{}` in `Print: {}`
   Print("Print: {}");
   return 0;
 }
diff --git a/explorer/testdata/print/fail_index_incomplete.carbon b/explorer/testdata/print/fail_index_incomplete.carbon
index 8e23072fa959..4292723016e3 100644
--- a/explorer/testdata/print/fail_index_incomplete.carbon
+++ b/explorer/testdata/print/fail_index_incomplete.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/print/fail_index_incomplete.carbon:[[@LINE+1]]: Index invalid with argument count of 0 at offset 8 in `Print: {0`
+  // CHECK:STDERR: RUNTIME ERROR: fail_index_incomplete.carbon:[[@LINE+1]]: Index invalid with argument count of 0 at offset 8 in `Print: {0`
   Print("Print: {0");
   return 0;
 }
diff --git a/explorer/testdata/print/fail_index_limit.carbon b/explorer/testdata/print/fail_index_limit.carbon
index 274f0da9e7c7..6081f079b395 100644
--- a/explorer/testdata/print/fail_index_limit.carbon
+++ b/explorer/testdata/print/fail_index_limit.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/print/fail_index_limit.carbon:[[@LINE+1]]: Index invalid with argument count of 0 at offset 8 in `Print: {2147483648}`
+  // CHECK:STDERR: RUNTIME ERROR: fail_index_limit.carbon:[[@LINE+1]]: Index invalid with argument count of 0 at offset 8 in `Print: {2147483648}`
   Print("Print: {2147483648}");
   return 0;
 }
diff --git a/explorer/testdata/print/fail_index_negative.carbon b/explorer/testdata/print/fail_index_negative.carbon
index 44f5d34a635f..97f6764b63b7 100644
--- a/explorer/testdata/print/fail_index_negative.carbon
+++ b/explorer/testdata/print/fail_index_negative.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/print/fail_index_negative.carbon:[[@LINE+1]]: Non-numeric character in index at offset 8 in `Print: {-1}`
+  // CHECK:STDERR: RUNTIME ERROR: fail_index_negative.carbon:[[@LINE+1]]: Non-numeric character in index at offset 8 in `Print: {-1}`
   Print("Print: {-1}");
   return 0;
 }
diff --git a/explorer/testdata/print/fail_index_text.carbon b/explorer/testdata/print/fail_index_text.carbon
index aedfdf25a9aa..0bb40c11bc09 100644
--- a/explorer/testdata/print/fail_index_text.carbon
+++ b/explorer/testdata/print/fail_index_text.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/print/fail_index_text.carbon:[[@LINE+1]]: Index invalid with argument count of 0 at offset 8 in `Print: {1a}`
+  // CHECK:STDERR: RUNTIME ERROR: fail_index_text.carbon:[[@LINE+1]]: Index invalid with argument count of 0 at offset 8 in `Print: {1a}`
   Print("Print: {1a}");
   return 0;
 }
diff --git a/explorer/testdata/print/fail_intrinsic_int_format.carbon b/explorer/testdata/print/fail_intrinsic_int_format.carbon
index 2f668992afc8..98075fbf195d 100644
--- a/explorer/testdata/print/fail_intrinsic_int_format.carbon
+++ b/explorer/testdata/print/fail_intrinsic_int_format.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/print/fail_intrinsic_int_format.carbon:[[@LINE+3]]: type error in Print argument 0
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_int_format.carbon:[[@LINE+3]]: type error in Print argument 0
   // CHECK:STDERR: expected: String
   // CHECK:STDERR: actual: i32
   __intrinsic_print(0);
diff --git a/explorer/testdata/print/fail_intrinsic_no_args.carbon b/explorer/testdata/print/fail_intrinsic_no_args.carbon
index b40ad78efb8a..454e1ea97ed8 100644
--- a/explorer/testdata/print/fail_intrinsic_no_args.carbon
+++ b/explorer/testdata/print/fail_intrinsic_no_args.carbon
@@ -7,6 +7,6 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/print/fail_intrinsic_no_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 0
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_no_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 0
   __intrinsic_print();
 }
diff --git a/explorer/testdata/print/fail_intrinsic_too_many_args.carbon b/explorer/testdata/print/fail_intrinsic_too_many_args.carbon
index 548c2763b552..b974b16b930d 100644
--- a/explorer/testdata/print/fail_intrinsic_too_many_args.carbon
+++ b/explorer/testdata/print/fail_intrinsic_too_many_args.carbon
@@ -7,6 +7,6 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/print/fail_intrinsic_too_many_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 4
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_too_many_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 4
   __intrinsic_print("", 1, 2, 3);
 }
diff --git a/explorer/testdata/print/fail_intrinsic_type.carbon b/explorer/testdata/print/fail_intrinsic_type.carbon
index 4f33dcdcc806..3c9f415a836d 100644
--- a/explorer/testdata/print/fail_intrinsic_type.carbon
+++ b/explorer/testdata/print/fail_intrinsic_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/print/fail_intrinsic_type.carbon:[[@LINE+3]]: type error in Print argument 1
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_type.carbon:[[@LINE+3]]: type error in Print argument 1
   // CHECK:STDERR: expected: i32
   // CHECK:STDERR: actual: {.x: i32}
   __intrinsic_print("{0}", {.x = 1});
diff --git a/explorer/testdata/print/fail_no_args.carbon b/explorer/testdata/print/fail_no_args.carbon
index aada5dc0aeae..eae6b5adefa7 100644
--- a/explorer/testdata/print/fail_no_args.carbon
+++ b/explorer/testdata/print/fail_no_args.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/print/fail_no_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 0
+  // CHECK:STDERR: COMPILATION ERROR: 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 b7b579d43d19..1ab161bde417 100644
--- a/explorer/testdata/print/fail_not_str.carbon
+++ b/explorer/testdata/print/fail_not_str.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/print/fail_not_str.carbon:[[@LINE+3]]: type error in Print argument 0
+  // CHECK:STDERR: COMPILATION ERROR: fail_not_str.carbon:[[@LINE+3]]: type error in Print argument 0
   // CHECK:STDERR: expected: String
   // CHECK:STDERR: actual: {.x: i32}
   Print({.x = 1});
diff --git a/explorer/testdata/print/fail_single_brace.carbon b/explorer/testdata/print/fail_single_brace.carbon
index b4a84d8f2d34..296d4d1132c3 100644
--- a/explorer/testdata/print/fail_single_brace.carbon
+++ b/explorer/testdata/print/fail_single_brace.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest impl;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/print/fail_single_brace.carbon:[[@LINE+1]]: `{` must be followed by a second `{` or index in `{`
+  // CHECK:STDERR: RUNTIME ERROR: fail_single_brace.carbon:[[@LINE+1]]: `{` must be followed by a second `{` or index in `{`
   Print("{");
   return 0;
 }
diff --git a/explorer/testdata/print/fail_too_many_args.carbon b/explorer/testdata/print/fail_too_many_args.carbon
index aca9ff254630..833b2252a3a2 100644
--- a/explorer/testdata/print/fail_too_many_args.carbon
+++ b/explorer/testdata/print/fail_too_many_args.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/print/fail_too_many_args.carbon:[[@LINE+1]]: Print takes 1 or 2 arguments, received 5
+  // CHECK:STDERR: COMPILATION ERROR: 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 7e07e47125bd..1944ea68fecb 100644
--- a/explorer/testdata/print/fail_type.carbon
+++ b/explorer/testdata/print/fail_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/print/fail_type.carbon:[[@LINE+3]]: type error in Print argument 1
+  // CHECK:STDERR: COMPILATION ERROR: fail_type.carbon:[[@LINE+3]]: type error in Print argument 1
   // CHECK:STDERR: expected: i32
   // CHECK:STDERR: actual: {.x: i32}
   Print("{0}", {.x = 1});
diff --git a/explorer/testdata/random/fail_empty_range.carbon b/explorer/testdata/random/fail_empty_range.carbon
index 17c6d1f7e18a..03b4c42e8317 100644
--- a/explorer/testdata/random/fail_empty_range.carbon
+++ b/explorer/testdata/random/fail_empty_range.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: Rand inputs must be ordered for a non-empty range: 0 must be less than 0
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: Rand inputs must be ordered for a non-empty range: 0 must be less than 0
 
 package ExplorerTest api;
 
diff --git a/explorer/testdata/random/fail_intrinsic_no_args.carbon b/explorer/testdata/random/fail_intrinsic_no_args.carbon
index 9c74b1a10adf..4da283e6479a 100644
--- a/explorer/testdata/random/fail_intrinsic_no_args.carbon
+++ b/explorer/testdata/random/fail_intrinsic_no_args.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/random/fail_intrinsic_no_args.carbon:[[@LINE+1]]: Rand takes 2 arguments, received 0
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_no_args.carbon:[[@LINE+1]]: Rand takes 2 arguments, received 0
   __intrinsic_rand();
   return 0;
 }
diff --git a/explorer/testdata/random/fail_intrinsic_type0.carbon b/explorer/testdata/random/fail_intrinsic_type0.carbon
index df31b5b5c65e..676dda607b38 100644
--- a/explorer/testdata/random/fail_intrinsic_type0.carbon
+++ b/explorer/testdata/random/fail_intrinsic_type0.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/random/fail_intrinsic_type0.carbon:[[@LINE+3]]: type error in Rand argument 0
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_type0.carbon:[[@LINE+3]]: type error in Rand argument 0
   // CHECK:STDERR: expected: i32
   // CHECK:STDERR: actual: String
   __intrinsic_rand("a", 1);
diff --git a/explorer/testdata/random/fail_intrinsic_type1.carbon b/explorer/testdata/random/fail_intrinsic_type1.carbon
index 82e0db3cfa7d..41314b79ad4f 100644
--- a/explorer/testdata/random/fail_intrinsic_type1.carbon
+++ b/explorer/testdata/random/fail_intrinsic_type1.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/random/fail_intrinsic_type1.carbon:[[@LINE+3]]: type error in Rand argument 1
+  // CHECK:STDERR: COMPILATION ERROR: fail_intrinsic_type1.carbon:[[@LINE+3]]: type error in Rand argument 1
   // CHECK:STDERR: expected: i32
   // CHECK:STDERR: actual: String
   __intrinsic_rand(1, "a");
diff --git a/explorer/testdata/random/fail_reverse_range.carbon b/explorer/testdata/random/fail_reverse_range.carbon
index cd90b7e3c295..23b782ea3b4c 100644
--- a/explorer/testdata/random/fail_reverse_range.carbon
+++ b/explorer/testdata/random/fail_reverse_range.carbon
@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDERR: RUNTIME ERROR: explorer/data/prelude.carbon:{{.*}}: Rand inputs must be ordered for a non-empty range: 1 must be less than -1
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: Rand inputs must be ordered for a non-empty range: 1 must be less than -1
 
 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 4628eb41de58..4c83d98b6729 100644
--- a/explorer/testdata/return/fail_explicit_with_no_return.carbon
+++ b/explorer/testdata/return/fail_explicit_with_no_return.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn F() -> () {
-// CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 0aee09373c39..72e58d0acbcc 100644
--- a/explorer/testdata/return/fail_explicit_with_plain_return.carbon
+++ b/explorer/testdata/return/fail_explicit_with_plain_return.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn F() -> () {
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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 79c962888d49..9557be4ee66a 100644
--- a/explorer/testdata/return/fail_implicit_with_explicit_return.carbon
+++ b/explorer/testdata/return/fail_implicit_with_explicit_return.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn F() {
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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/string/fail_block_quotes_not_on_own_line.carbon b/explorer/testdata/string/fail_block_quotes_not_on_own_line.carbon
index b83605f93dc0..ce0ba783896e 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
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: 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:STDERR: SYNTAX ERROR: 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 2d358fc30fce..b2999c35ff81 100644
--- a/explorer/testdata/string/fail_hex_lower.carbon
+++ b/explorer/testdata/string/fail_hex_lower.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_hex_lower.carbon:[[@LINE+1]]: Invalid escaping in string: "str\xaa"
+  // CHECK:STDERR: SYNTAX ERROR: 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 e05fb935ce43..e514f33b8761 100644
--- a/explorer/testdata/string/fail_hex_truncated.carbon
+++ b/explorer/testdata/string/fail_hex_truncated.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_hex_truncated.carbon:[[@LINE+1]]: Invalid escaping in string: "str\x"
+  // CHECK:STDERR: SYNTAX ERROR: 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 f36140407b0d..92779c95c32a 100644
--- a/explorer/testdata/string/fail_invalid_escape.carbon
+++ b/explorer/testdata/string/fail_invalid_escape.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_invalid_escape.carbon:[[@LINE+1]]: Invalid escaping in string: "str\e"
+  // CHECK:STDERR: SYNTAX ERROR: 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 4b1075b632e5..eee03b2060b2 100644
--- a/explorer/testdata/string/fail_newline.carbon
+++ b/explorer/testdata/string/fail_newline.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_newline.carbon:[[@LINE+2]]: missing closing quote in single-line string: "new
+  // CHECK:STDERR: SYNTAX ERROR: fail_newline.carbon:[[@LINE+2]]: missing closing quote in single-line string: "new
   // CHECK:STDERR:
   Print("new
 line");
diff --git a/explorer/testdata/string/fail_octal.carbon b/explorer/testdata/string/fail_octal.carbon
index 5d91cede8dc2..92caffe5e46a 100644
--- a/explorer/testdata/string/fail_octal.carbon
+++ b/explorer/testdata/string/fail_octal.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_octal.carbon:[[@LINE+1]]: Invalid escaping in string: "str\01"
+  // CHECK:STDERR: SYNTAX ERROR: 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 9afbffd9c199..6135a7d337b6 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
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_raw_block_more_hash_tags_on_left.carbon:[[@LINE+1]]: Unexpected end of file
+  // CHECK:STDERR: SYNTAX ERROR: 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 45de606b26b8..b51098000623 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
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_raw_block_more_hash_tags_on_right.carbon:[[@LINE+1]]: invalid character '\x23' in source file.
+  // CHECK:STDERR: SYNTAX ERROR: 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 191944b79823..23dbe9af936a 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
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: 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:STDERR: SYNTAX ERROR: 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 56564514e5bc..f8b6c2d0248b 100644
--- a/explorer/testdata/string/fail_raw_block_single_line.carbon
+++ b/explorer/testdata/string/fail_raw_block_single_line.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn CompareStr(s: String) -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_raw_block_single_line.carbon:[[@LINE+1]]: Invalid block string: Too few lines
+  // CHECK:STDERR: SYNTAX ERROR: 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 1bb1cf30035f..1ee9af4849de 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
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn CompareStr(s: String) -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_raw_more_hash_tags_on_left.carbon:[[@LINE+2]]: missing closing quote in single-line string: ##"str"#) {
+  // CHECK:STDERR: SYNTAX ERROR: fail_raw_more_hash_tags_on_left.carbon:[[@LINE+2]]: missing closing quote in single-line string: ##"str"#) {
   // CHECK:STDERR:
   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 664385413681..60c3219664ec 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
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn CompareStr(s: String) -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_raw_more_hash_tags_on_right.carbon:[[@LINE+1]]: invalid character '\x23' in source file.
+  // CHECK:STDERR: SYNTAX ERROR: 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 b541fa84650e..87b7f8b0381b 100644
--- a/explorer/testdata/string/fail_tab.carbon
+++ b/explorer/testdata/string/fail_tab.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/string/fail_tab.carbon:[[@LINE+1]]: Invalid escaping in string: "new	line"
+  // CHECK:STDERR: SYNTAX ERROR: fail_tab.carbon:[[@LINE+1]]: Invalid escaping in string: "new	line"
   Print("new	line");
   return 0;
 }
diff --git a/explorer/testdata/struct/fail_assign_different_types.carbon b/explorer/testdata/struct/fail_assign_different_types.carbon
index 5741052a91e3..3d2afd618691 100644
--- a/explorer/testdata/struct/fail_assign_different_types.carbon
+++ b/explorer/testdata/struct/fail_assign_different_types.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var p: auto = {.x = 0, .y = 0};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/struct/fail_assign_different_types.carbon:[[@LINE+1]]: could not find implementation of interface AssignWith(U = {.y: i32}) for {.x: i32, .y: i32}
+  // CHECK:STDERR: COMPILATION ERROR: fail_assign_different_types.carbon:[[@LINE+1]]: could not find implementation of interface AssignWith(U = {.y: i32}) for {.x: i32, .y: i32}
   p = {.y = 0};
   return 0;
 }
diff --git a/explorer/testdata/struct/fail_equality_type.carbon b/explorer/testdata/struct/fail_equality_type.carbon
index 0f257bd9e146..6d9e4c050a75 100644
--- a/explorer/testdata/struct/fail_equality_type.carbon
+++ b/explorer/testdata/struct/fail_equality_type.carbon
@@ -19,7 +19,7 @@ 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:STDERR: 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:STDERR: COMPILATION ERROR: 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 e9008f5be06f..7be933254ee3 100644
--- a/explorer/testdata/struct/fail_field_access_mismatch.carbon
+++ b/explorer/testdata/struct/fail_field_access_mismatch.carbon
@@ -7,6 +7,6 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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/fail_struct_literal_duplicate_member.carbon b/explorer/testdata/struct/fail_struct_literal_duplicate_member.carbon
index adf9f55e1f32..8d2b4889bdd7 100644
--- a/explorer/testdata/struct/fail_struct_literal_duplicate_member.carbon
+++ b/explorer/testdata/struct/fail_struct_literal_duplicate_member.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/struct/fail_struct_literal_duplicate_member.carbon:[[@LINE+1]]: Duplicate name `x` in struct literal
+  // CHECK:STDERR: COMPILATION ERROR: fail_struct_literal_duplicate_member.carbon:[[@LINE+1]]: Duplicate name `x` in struct literal
   var x: auto = {.x = 0, .x = 0};
   return 0;
 }
diff --git a/explorer/testdata/struct/fail_struct_type_literal_duplicate_member.carbon b/explorer/testdata/struct/fail_struct_type_literal_duplicate_member.carbon
index c4674f3fc873..9aeeb35cc85a 100644
--- a/explorer/testdata/struct/fail_struct_type_literal_duplicate_member.carbon
+++ b/explorer/testdata/struct/fail_struct_type_literal_duplicate_member.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/struct/fail_struct_type_literal_duplicate_member.carbon:[[@LINE+1]]: Duplicate name `x` in struct type literal
+  // CHECK:STDERR: COMPILATION ERROR: fail_struct_type_literal_duplicate_member.carbon:[[@LINE+1]]: Duplicate name `x` in struct type literal
   var y: {.x: i32, .x: i32};
   return 0;
 }
diff --git a/explorer/testdata/template/fail_name_lookup.carbon b/explorer/testdata/template/fail_name_lookup.carbon
index 4b4faa96a169..5a02bb3c4605 100644
--- a/explorer/testdata/template/fail_name_lookup.carbon
+++ b/explorer/testdata/template/fail_name_lookup.carbon
@@ -17,7 +17,7 @@ interface HasF {
 impl forall [template T:! HasF] T as CallF {
   // TODO: This case should be accepted, using `ClassWithExternalF.(HasF.F)`.
   // TODO: The other case should be rejected due to ambiguity.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/template/fail_name_lookup.carbon:[[@LINE+1]]: class ClassWithExternalF does not have a field named F
+  // CHECK:STDERR: COMPILATION ERROR: fail_name_lookup.carbon:[[@LINE+1]]: class ClassWithExternalF does not have a field named F
   fn DoIt[self: Self]() { self.F(); }
 }
 
diff --git a/explorer/testdata/template/fail_no_member.carbon b/explorer/testdata/template/fail_no_member.carbon
index 9a55b443a27b..45a45711100f 100644
--- a/explorer/testdata/template/fail_no_member.carbon
+++ b/explorer/testdata/template/fail_no_member.carbon
@@ -11,7 +11,7 @@ interface GetX {
 }
 
 impl forall [template T:! type] T as GetX {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/template/fail_no_member.carbon:[[@LINE+1]]: member access, unexpected i32 in self.x
+  // CHECK:STDERR: COMPILATION ERROR: fail_no_member.carbon:[[@LINE+1]]: member access, unexpected i32 in self.x
   fn DoIt[self: Self]() -> i32 { return self.x; }
 }
 
diff --git a/explorer/testdata/tuple/fail_equality_type.carbon b/explorer/testdata/tuple/fail_equality_type.carbon
index 37fa704d9b47..f218bd04a52a 100644
--- a/explorer/testdata/tuple/fail_equality_type.carbon
+++ b/explorer/testdata/tuple/fail_equality_type.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var t1: (i32, i32) = (5, 2);
   var t2: (i32,) = (5,);
-  // CHECK:STDERR: 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:STDERR: COMPILATION ERROR: 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_implicit_convert_with_as.carbon b/explorer/testdata/tuple/fail_implicit_convert_with_as.carbon
index 6178d3ba6bdd..7f6167ff7f49 100644
--- a/explorer/testdata/tuple/fail_implicit_convert_with_as.carbon
+++ b/explorer/testdata/tuple/fail_implicit_convert_with_as.carbon
@@ -19,7 +19,7 @@ external impl A as As(B) {
 
 fn Main() -> i32 {
   var a: (i32, A) = (1, {.a = 2});
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/tuple/fail_implicit_convert_with_as.carbon:[[@LINE+1]]: type error in initializer of variable: '(i32, class A)' is not implicitly convertible to '(i32, class B)'
+  // CHECK:STDERR: COMPILATION ERROR: fail_implicit_convert_with_as.carbon:[[@LINE+1]]: type error in initializer of variable: '(i32, class A)' is not implicitly convertible to '(i32, class B)'
   var b: (i32, B) = a;
   return b[1].b;
 }
diff --git a/explorer/testdata/tuple/fail_index.carbon b/explorer/testdata/tuple/fail_index.carbon
index 296e1ee61658..97724e7acf6c 100644
--- a/explorer/testdata/tuple/fail_index.carbon
+++ b/explorer/testdata/tuple/fail_index.carbon
@@ -8,6 +8,6 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: auto = (0, 1);
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/tuple/fail_index.carbon:[[@LINE+1]]: index 2 is out of range for type (i32, i32)
+  // CHECK:STDERR: COMPILATION ERROR: 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 9df2fd737b7e..48bdd79c8b5e 100644
--- a/explorer/testdata/tuple/fail_index_var.carbon
+++ b/explorer/testdata/tuple/fail_index_var.carbon
@@ -9,6 +9,6 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: auto = (0, 1);
   var index: i32 = 0;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/tuple/fail_index_var.carbon:[[@LINE+1]]: could not find `index: i32`
+  // CHECK:STDERR: COMPILATION ERROR: fail_index_var.carbon:[[@LINE+1]]: could not find `index: i32`
   return x[index];
 }
diff --git a/explorer/testdata/tuple/fail_length_mismatch_with_auto.carbon b/explorer/testdata/tuple/fail_length_mismatch_with_auto.carbon
index 54faa1681cc5..e85d200c0182 100644
--- a/explorer/testdata/tuple/fail_length_mismatch_with_auto.carbon
+++ b/explorer/testdata/tuple/fail_length_mismatch_with_auto.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/tuple/fail_length_mismatch_with_auto.carbon:[[@LINE+1]]: tuples of different length
+  // CHECK:STDERR: COMPILATION ERROR: fail_length_mismatch_with_auto.carbon:[[@LINE+1]]: tuples of different length
   var a: (auto,) = (1, 2);
   return 0;
 }
diff --git a/explorer/testdata/tuple/fail_nontype_tuple_as_type.carbon b/explorer/testdata/tuple/fail_nontype_tuple_as_type.carbon
index 41304af717ba..9816b7c8dc4c 100644
--- a/explorer/testdata/tuple/fail_nontype_tuple_as_type.carbon
+++ b/explorer/testdata/tuple/fail_nontype_tuple_as_type.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/tuple/fail_nontype_tuple_as_type.carbon:[[@LINE+1]]: type error in type of name binding: '(i32, i32)' is not implicitly convertible to 'type'
+// CHECK:STDERR: COMPILATION ERROR: fail_nontype_tuple_as_type.carbon:[[@LINE+1]]: type error in type of name binding: '(i32, i32)' is not implicitly convertible to 'type'
 fn F[T:! (i32, i32)](x: T);
 
 fn Main() -> i32;
diff --git a/explorer/testdata/tuple/fail_to_array.carbon b/explorer/testdata/tuple/fail_to_array.carbon
index 1e08c13d64e1..42ad4f5b680b 100644
--- a/explorer/testdata/tuple/fail_to_array.carbon
+++ b/explorer/testdata/tuple/fail_to_array.carbon
@@ -8,6 +8,6 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var t: auto = (1, 2);
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/tuple/fail_to_array.carbon:[[@LINE+1]]: type error in initializer of variable: '(i32, i32)' is not implicitly convertible to '[i32; 3]'
+  // CHECK:STDERR: COMPILATION ERROR: fail_to_array.carbon:[[@LINE+1]]: type error in initializer of variable: '(i32, i32)' is not implicitly convertible to '[i32; 3]'
   var a: [i32; 3] = t;
 }
diff --git a/explorer/testdata/tuple/fail_type_tuple_as_type.carbon b/explorer/testdata/tuple/fail_type_tuple_as_type.carbon
index 8b1946348e7e..cd1065fbd269 100644
--- a/explorer/testdata/tuple/fail_type_tuple_as_type.carbon
+++ b/explorer/testdata/tuple/fail_type_tuple_as_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn F[T:! ((), ())](x: T) -> () {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/tuple/fail_type_tuple_as_type.carbon:[[@LINE+1]]: only arrays and tuples can be indexed, found T
+  // CHECK:STDERR: COMPILATION ERROR: fail_type_tuple_as_type.carbon:[[@LINE+1]]: only arrays and tuples can be indexed, found T
   return x[0];
 }
 
diff --git a/explorer/testdata/tuple/fail_unexpected_tuple.carbon b/explorer/testdata/tuple/fail_unexpected_tuple.carbon
index 3d8b55f85bc8..4f52cd2d48b9 100644
--- a/explorer/testdata/tuple/fail_unexpected_tuple.carbon
+++ b/explorer/testdata/tuple/fail_unexpected_tuple.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/tuple/fail_unexpected_tuple.carbon:[[@LINE+1]]: didn't expect a tuple
+  // CHECK:STDERR: COMPILATION ERROR: fail_unexpected_tuple.carbon:[[@LINE+1]]: didn't expect a tuple
   var a: (auto,) = 1;
   return 0;
 }
diff --git a/explorer/testdata/unformed/dynamic/fail_global.carbon b/explorer/testdata/unformed/dynamic/fail_global.carbon
index b72b0c8bf82c..50d5d3a51b25 100644
--- a/explorer/testdata/unformed/dynamic/fail_global.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_global.carbon
@@ -9,6 +9,6 @@ package ExplorerTest api;
 var x: i32;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/unformed/dynamic/fail_global.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:STDERR: RUNTIME ERROR: 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 c4a7a6f429de..b6b508dffa25 100644
--- a/explorer/testdata/unformed/dynamic/fail_param.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_param.carbon
@@ -16,6 +16,6 @@ fn Main() -> i32 {
     x = 0;
   }
   // Static analysis thinks `x` may be formed, defer the check to run-time.
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/unformed/dynamic/fail_param.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:STDERR: RUNTIME ERROR: 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 4ff0fd52afc1..3b4e23f0f5df 100644
--- a/explorer/testdata/unformed/dynamic/fail_pattern_declare.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_pattern_declare.carbon
@@ -13,6 +13,6 @@ fn Main() -> i32 {
     y = 0;
   }
   // Static analysis thinks `y` may be formed, defer the check to run-time.
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/unformed/dynamic/fail_pattern_declare.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<y>>
+  // CHECK:STDERR: RUNTIME ERROR: 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 5b4c0b8aceb2..bf85bb7f0538 100644
--- a/explorer/testdata/unformed/dynamic/fail_return.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_return.carbon
@@ -12,6 +12,6 @@ fn Main() -> i32 {
     x = 0;
   }
   // Static analysis thinks `x` may be formed, defer the check to run-time.
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/unformed/dynamic/fail_return.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:STDERR: RUNTIME ERROR: 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 f5832cd88ae4..788ce308bd30 100644
--- a/explorer/testdata/unformed/dynamic/fail_returned_var.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_returned_var.carbon
@@ -12,6 +12,6 @@ fn Main() -> i32 {
     x = 0;
   }
   // Static analysis thinks `x` may be formed, defer the check to run-time.
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/unformed/dynamic/fail_returned_var.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:STDERR: RUNTIME ERROR: 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 d0e13d6964fc..87a16e6e0962 100644
--- a/explorer/testdata/unformed/dynamic/fail_rhs_assign.carbon
+++ b/explorer/testdata/unformed/dynamic/fail_rhs_assign.carbon
@@ -13,7 +13,7 @@ fn Main() -> i32 {
     x = 0;
   }
   // Static analysis thinks `x` may be formed, defer the check to run-time.
-  // CHECK:STDERR: RUNTIME ERROR: explorer/testdata/unformed/dynamic/fail_rhs_assign.carbon:[[@LINE+1]]: undefined behavior: access to uninitialized value Uninit<Placeholder<x>>
+  // CHECK:STDERR: RUNTIME ERROR: 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/static/fail_compound_assign.carbon b/explorer/testdata/unformed/static/fail_compound_assign.carbon
index 62f115cd6664..e125ccb7cf43 100644
--- a/explorer/testdata/unformed/static/fail_compound_assign.carbon
+++ b/explorer/testdata/unformed/static/fail_compound_assign.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_compound_assign.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: fail_compound_assign.carbon:[[@LINE+1]]: use of uninitialized variable x
   x += 1;
   return x;
 }
diff --git a/explorer/testdata/unformed/static/fail_field_value.carbon b/explorer/testdata/unformed/static/fail_field_value.carbon
index b32b9c0a79d2..60a2677ef4b1 100644
--- a/explorer/testdata/unformed/static/fail_field_value.carbon
+++ b/explorer/testdata/unformed/static/fail_field_value.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_field_value.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: 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 e9611b6e252d..e2df26c2ec43 100644
--- a/explorer/testdata/unformed/static/fail_if_cond.carbon
+++ b/explorer/testdata/unformed/static/fail_if_cond.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_if_cond.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: 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 9ffb9fa20197..6d53b9f5cbb8 100644
--- a/explorer/testdata/unformed/static/fail_if_else.carbon
+++ b/explorer/testdata/unformed/static/fail_if_else.carbon
@@ -13,7 +13,7 @@ fn Main() -> i32 {
   if (Foo() == 0) {
     return 0;
   } else {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_if_else.carbon:[[@LINE+1]]: use of uninitialized variable x
+    // CHECK:STDERR: COMPILATION ERROR: 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 5a21dc247d19..19bb75997317 100644
--- a/explorer/testdata/unformed/static/fail_if_then.carbon
+++ b/explorer/testdata/unformed/static/fail_if_then.carbon
@@ -11,7 +11,7 @@ fn Foo() -> i32;
 fn Main() -> i32 {
   var x: i32;
   if (Foo() == 0) {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_if_then.carbon:[[@LINE+1]]: use of uninitialized variable x
+    // CHECK:STDERR: COMPILATION ERROR: fail_if_then.carbon:[[@LINE+1]]: use of uninitialized variable x
     return x;
   }
   return 1;
diff --git a/explorer/testdata/unformed/static/fail_increment.carbon b/explorer/testdata/unformed/static/fail_increment.carbon
index 522211cd079d..aa3905ca0255 100644
--- a/explorer/testdata/unformed/static/fail_increment.carbon
+++ b/explorer/testdata/unformed/static/fail_increment.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_increment.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: fail_increment.carbon:[[@LINE+1]]: use of uninitialized variable x
   ++x;
   return x;
 }
diff --git a/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon b/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon
index 6910a36e2c28..baa59d8aefc9 100644
--- a/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon
+++ b/explorer/testdata/unformed/static/fail_local_pattern_declare.carbon
@@ -9,6 +9,6 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var (x: i32, y: i32);
   x = 1;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_local_pattern_declare.carbon:[[@LINE+1]]: use of uninitialized variable y
+  // CHECK:STDERR: COMPILATION ERROR: 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 15c0d67e8e9c..449bb9fe10c4 100644
--- a/explorer/testdata/unformed/static/fail_local_rhs_assign.carbon
+++ b/explorer/testdata/unformed/static/fail_local_rhs_assign.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn Main() -> i32 {
   var x: i32;
   var y: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_local_rhs_assign.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: 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 497c17f30c0a..e16b90b189ef 100644
--- a/explorer/testdata/unformed/static/fail_match_clause.carbon
+++ b/explorer/testdata/unformed/static/fail_match_clause.carbon
@@ -15,7 +15,7 @@ fn Main() -> i32 {
       return 2;
     }
     case 1 => {
-      // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_match_clause.carbon:[[@LINE+1]]: use of uninitialized variable x
+      // CHECK:STDERR: COMPILATION ERROR: 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 fa3f44943cda..edcfbd4a45ff 100644
--- a/explorer/testdata/unformed/static/fail_match_expression.carbon
+++ b/explorer/testdata/unformed/static/fail_match_expression.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x : i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_match_expression.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: 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 b38caad24517..43de0f18f190 100644
--- a/explorer/testdata/unformed/static/fail_param.carbon
+++ b/explorer/testdata/unformed/static/fail_param.carbon
@@ -12,6 +12,6 @@ fn AddInt(a: i32, b: i32) -> auto {
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_param.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: 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 5a7db2c5e8f9..d7df4fa0cd2d 100644
--- a/explorer/testdata/unformed/static/fail_return.carbon
+++ b/explorer/testdata/unformed/static/fail_return.carbon
@@ -8,6 +8,6 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_return.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: 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 277466641f23..cbf41523d15e 100644
--- a/explorer/testdata/unformed/static/fail_returned_var.carbon
+++ b/explorer/testdata/unformed/static/fail_returned_var.carbon
@@ -8,6 +8,6 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   returned var x: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_returned_var.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: 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 3ff379a52443..9e166d23cc84 100644
--- a/explorer/testdata/unformed/static/fail_rhs_def.carbon
+++ b/explorer/testdata/unformed/static/fail_rhs_def.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: i32;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_rhs_def.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: 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 0bfcaea29ca3..185cfa79e376 100644
--- a/explorer/testdata/unformed/static/fail_struct_member_access.carbon
+++ b/explorer/testdata/unformed/static/fail_struct_member_access.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var p: {.x: i32, .y: i32};
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_struct_member_access.carbon:[[@LINE+1]]: use of uninitialized variable p
+  // CHECK:STDERR: COMPILATION ERROR: 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 b9f3c6a8e12d..c0ff72802991 100644
--- a/explorer/testdata/unformed/static/fail_while_body.carbon
+++ b/explorer/testdata/unformed/static/fail_while_body.carbon
@@ -11,7 +11,7 @@ fn Foo() -> i32;
 fn Main() -> i32 {
   var (x: i32, y: i32);
   while (Foo() == 0) {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_while_body.carbon:[[@LINE+1]]: use of uninitialized variable x
+    // CHECK:STDERR: COMPILATION ERROR: 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 a696f175a937..95a4fd8449ad 100644
--- a/explorer/testdata/unformed/static/fail_while_cond.carbon
+++ b/explorer/testdata/unformed/static/fail_while_cond.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   var (x: i32, y: i32);
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/unformed/static/fail_while_cond.carbon:[[@LINE+1]]: use of uninitialized variable x
+  // CHECK:STDERR: COMPILATION ERROR: fail_while_cond.carbon:[[@LINE+1]]: use of uninitialized variable x
   while (x == 0) {
     y = 1;
   }
diff --git a/explorer/testdata/var/global/fail_init_type_mismatch.carbon b/explorer/testdata/var/global/fail_init_type_mismatch.carbon
index 7b7fd5ab2ce0..7e8945e11ec0 100644
--- a/explorer/testdata/var/global/fail_init_type_mismatch.carbon
+++ b/explorer/testdata/var/global/fail_init_type_mismatch.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 // Test type checking of global variable. Error expected.
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/global/fail_init_type_mismatch.carbon:[[@LINE+1]]: type error in initializer of variable: 'bool' is not implicitly convertible to 'i32'
+// CHECK:STDERR: COMPILATION ERROR: 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/var/global/fail_instantiate_global_abstract.carbon b/explorer/testdata/var/global/fail_instantiate_global_abstract.carbon
index d7b4ab0c93bf..ecd4920bb8d2 100644
--- a/explorer/testdata/var/global/fail_instantiate_global_abstract.carbon
+++ b/explorer/testdata/var/global/fail_instantiate_global_abstract.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 abstract class B {
 }
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/global/fail_instantiate_global_abstract.carbon:[[@LINE+1]]: Cannot instantiate abstract class B
+// CHECK:STDERR: COMPILATION ERROR: fail_instantiate_global_abstract.carbon:[[@LINE+1]]: Cannot instantiate abstract class B
 var b: B = {};
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/var/global/fail_invalid_var_expression.carbon b/explorer/testdata/var/global/fail_invalid_var_expression.carbon
index 07737bd28721..96636bcb69f2 100644
--- a/explorer/testdata/var/global/fail_invalid_var_expression.carbon
+++ b/explorer/testdata/var/global/fail_invalid_var_expression.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/global/fail_invalid_var_expression.carbon:[[@LINE+1]]: Expected expression for variable type
+// CHECK:STDERR: COMPILATION ERROR: 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/var/global/fail_modify_in_constant_expr.carbon b/explorer/testdata/var/global/fail_modify_in_constant_expr.carbon
index 58d3407c94c7..ea58637db62d 100644
--- a/explorer/testdata/var/global/fail_modify_in_constant_expr.carbon
+++ b/explorer/testdata/var/global/fail_modify_in_constant_expr.carbon
@@ -11,7 +11,7 @@ var n: i32 = 0;
 fn F() -> type {
   // TODO: This isn't a very good description of the problem, which is that
   // compile-time evaluation doesn't have a mutable `n` value available.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/global/fail_modify_in_constant_expr.carbon:[[@LINE+1]]: could not find `n: i32`
+  // CHECK:STDERR: COMPILATION ERROR: fail_modify_in_constant_expr.carbon:[[@LINE+1]]: could not find `n: i32`
   n = 1;
   return i32;
 }
diff --git a/explorer/testdata/var/global/fail_named_self.carbon b/explorer/testdata/var/global/fail_named_self.carbon
index 487492d4e38f..79b8fc7ad2a2 100644
--- a/explorer/testdata/var/global/fail_named_self.carbon
+++ b/explorer/testdata/var/global/fail_named_self.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 // Error: global variable may not be named with keyword `Self`.
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/var/global/fail_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
+// CHECK:STDERR: SYNTAX ERROR: fail_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
 var Self: i32 = 0;
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/var/global/fail_nested_binding.carbon b/explorer/testdata/var/global/fail_nested_binding.carbon
index dc9cb2ac3ce0..43e8a67aa8ed 100644
--- a/explorer/testdata/var/global/fail_nested_binding.carbon
+++ b/explorer/testdata/var/global/fail_nested_binding.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 // If support for this is added, it'll be necessary to verify that either the
 // implementation is shared with locals or that tests are copied over for edge
 // cases.
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/var/global/fail_nested_binding.carbon:[[@LINE+1]]: syntax error, unexpected LEFT_PARENTHESIS, expecting identifier
+// CHECK:STDERR: SYNTAX ERROR: fail_nested_binding.carbon:[[@LINE+1]]: syntax error, unexpected LEFT_PARENTHESIS, expecting identifier
 var (x: i32,);
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/var/global/fail_type_only.carbon b/explorer/testdata/var/global/fail_type_only.carbon
index 52161375ca17..e3b25211575b 100644
--- a/explorer/testdata/var/global/fail_type_only.carbon
+++ b/explorer/testdata/var/global/fail_type_only.carbon
@@ -6,7 +6,7 @@
 
 package ExplorerTest api;
 
-// CHECK:STDERR: SYNTAX ERROR: explorer/testdata/var/global/fail_type_only.carbon:[[@LINE+1]]: syntax error, unexpected sized_type_literal, expecting identifier
+// CHECK:STDERR: SYNTAX ERROR: fail_type_only.carbon:[[@LINE+1]]: syntax error, unexpected sized_type_literal, expecting identifier
 var i32;
 
 fn Main() -> i32 {
diff --git a/explorer/testdata/var/local/fail_generic_binding_in_type.carbon b/explorer/testdata/var/local/fail_generic_binding_in_type.carbon
index 7299b276fce2..508f23d366f7 100644
--- a/explorer/testdata/var/local/fail_generic_binding_in_type.carbon
+++ b/explorer/testdata/var/local/fail_generic_binding_in_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/local/fail_generic_binding_in_type.carbon:[[@LINE+1]]: Binding types cannot contain bindings, but `T:! type` is a binding.
+  // CHECK:STDERR: COMPILATION ERROR: fail_generic_binding_in_type.carbon:[[@LINE+1]]: Binding types cannot contain bindings, but `T:! type` is a binding.
   var x: (T:! type) = 1;
   return 1;
 }
diff --git a/explorer/testdata/var/local/fail_missing_intro.carbon b/explorer/testdata/var/local/fail_missing_intro.carbon
index 74680a534b6f..7421da8fafd3 100644
--- a/explorer/testdata/var/local/fail_missing_intro.carbon
+++ b/explorer/testdata/var/local/fail_missing_intro.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: SYNTAX ERROR: explorer/testdata/var/local/fail_missing_intro.carbon:[[@LINE+1]]: syntax error, unexpected COLON
+  // CHECK:STDERR: SYNTAX ERROR: fail_missing_intro.carbon:[[@LINE+1]]: syntax error, unexpected COLON
   x: i32;
   return 1;
 }
diff --git a/explorer/testdata/var/local/fail_named_self_type.carbon b/explorer/testdata/var/local/fail_named_self_type.carbon
index 03272150da2a..8591cdfd2608 100644
--- a/explorer/testdata/var/local/fail_named_self_type.carbon
+++ b/explorer/testdata/var/local/fail_named_self_type.carbon
@@ -10,7 +10,7 @@ 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:STDERR: SYNTAX ERROR: explorer/testdata/var/local/fail_named_self_type.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting EQUAL or SEMICOLON
+  // CHECK:STDERR: SYNTAX ERROR: fail_named_self_type.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting EQUAL or SEMICOLON
   var Self: i32 = 0;
   return 0;
 }
diff --git a/explorer/testdata/var/local/fail_nested_binding_in_type.carbon b/explorer/testdata/var/local/fail_nested_binding_in_type.carbon
index d7a8142cf33f..214ca92dc6e3 100644
--- a/explorer/testdata/var/local/fail_nested_binding_in_type.carbon
+++ b/explorer/testdata/var/local/fail_nested_binding_in_type.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/local/fail_nested_binding_in_type.carbon:[[@LINE+1]]: Binding types cannot contain bindings, but `T: type` is a binding.
+  // CHECK:STDERR: COMPILATION ERROR: fail_nested_binding_in_type.carbon:[[@LINE+1]]: Binding types cannot contain bindings, but `T: type` is a binding.
   var x: (T: type) = 1;
   return 1;
 }
diff --git a/explorer/testdata/var/local/fail_nested_type_only.carbon b/explorer/testdata/var/local/fail_nested_type_only.carbon
index a20aa3faf277..4559115974fc 100644
--- a/explorer/testdata/var/local/fail_nested_type_only.carbon
+++ b/explorer/testdata/var/local/fail_nested_type_only.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/local/fail_nested_type_only.carbon:[[@LINE+1]]: An irrefutable pattern is required, but `i32` is refutable.
+  // CHECK:STDERR: COMPILATION ERROR: fail_nested_type_only.carbon:[[@LINE+1]]: An irrefutable pattern is required, but `i32` is refutable.
   var (x: i32, i32);
   return 0;
 }
diff --git a/explorer/testdata/var/local/fail_type_only.carbon b/explorer/testdata/var/local/fail_type_only.carbon
index 2c1b2958df1d..cadb7e29ad64 100644
--- a/explorer/testdata/var/local/fail_type_only.carbon
+++ b/explorer/testdata/var/local/fail_type_only.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/local/fail_type_only.carbon:[[@LINE+1]]: An irrefutable pattern is required, but `i32` is refutable.
+  // CHECK:STDERR: COMPILATION ERROR: fail_type_only.carbon:[[@LINE+1]]: An irrefutable pattern is required, but `i32` is refutable.
   var i32;
   return 0;
 }
diff --git a/explorer/testdata/var/local/fail_value_as_type.carbon b/explorer/testdata/var/local/fail_value_as_type.carbon
index dbee3daeef4f..69d3c9f36214 100644
--- a/explorer/testdata/var/local/fail_value_as_type.carbon
+++ b/explorer/testdata/var/local/fail_value_as_type.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Main() -> i32 {
   // 42 cannot be used as the type of a variable.
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/local/fail_value_as_type.carbon:[[@LINE+1]]: type error in type of name binding: 'i32' is not implicitly convertible to 'type'
+  // CHECK:STDERR: COMPILATION ERROR: fail_value_as_type.carbon:[[@LINE+1]]: type error in type of name binding: 'i32' is not implicitly convertible to 'type'
   var x: 42 = 0;
   return x;
 }
diff --git a/explorer/testdata/var/returned/fail_duplicate_return_var.carbon b/explorer/testdata/var/returned/fail_duplicate_return_var.carbon
index 520a7789afbf..dba2407b5d14 100644
--- a/explorer/testdata/var/returned/fail_duplicate_return_var.carbon
+++ b/explorer/testdata/var/returned/fail_duplicate_return_var.carbon
@@ -9,7 +9,7 @@ package ExplorerTest api;
 fn AddInt(a: i32, b: i32) -> i32 {
   returned var ret: i32 = a + b;
   if (a == b) {
-    // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/returned/fail_duplicate_return_var.carbon:[[@LINE+1]]: Duplicate definition of returned var also found at explorer/testdata/var/returned/fail_duplicate_return_var.carbon:[[@LINE-2]]
+    // CHECK:STDERR: COMPILATION ERROR: fail_duplicate_return_var.carbon:[[@LINE+1]]: Duplicate definition of returned var also found at fail_duplicate_return_var.carbon:[[@LINE-2]]
     returned var ret2: i32 = a + b;
   }
   return var;
diff --git a/explorer/testdata/var/returned/fail_missing_declaration.carbon b/explorer/testdata/var/returned/fail_missing_declaration.carbon
index 475d9dbb8ffe..90325a188f24 100644
--- a/explorer/testdata/var/returned/fail_missing_declaration.carbon
+++ b/explorer/testdata/var/returned/fail_missing_declaration.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn AddInt(a: i32, b: i32) -> i32 {
   var ret: i32 = a + b;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/returned/fail_missing_declaration.carbon:[[@LINE+1]]: `return var` is not allowed without a returned var defined in scope.
+  // CHECK:STDERR: COMPILATION ERROR: 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/var/returned/fail_missing_return.carbon b/explorer/testdata/var/returned/fail_missing_return.carbon
index dda3aa5d2d63..52c258592a83 100644
--- a/explorer/testdata/var/returned/fail_missing_return.carbon
+++ b/explorer/testdata/var/returned/fail_missing_return.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn AddInt(a: i32, b: i32) -> i32 {
   returned var ret: i32 = a + b;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/returned/fail_missing_return.carbon:[[@LINE+1]]: `return <expression>` is not allowed with a returned var defined in scope: explorer/testdata/var/returned/fail_missing_return.carbon:[[@LINE-1]]
+  // CHECK:STDERR: COMPILATION ERROR: fail_missing_return.carbon:[[@LINE+1]]: `return <expression>` is not allowed with a returned var defined in scope: fail_missing_return.carbon:[[@LINE-1]]
   return ret;
 }
 
diff --git a/explorer/testdata/var/returned/fail_returned_var_mismatch_signature.carbon b/explorer/testdata/var/returned/fail_returned_var_mismatch_signature.carbon
index c73221abc6f8..62fa718b083c 100644
--- a/explorer/testdata/var/returned/fail_returned_var_mismatch_signature.carbon
+++ b/explorer/testdata/var/returned/fail_returned_var_mismatch_signature.carbon
@@ -8,7 +8,7 @@ package ExplorerTest api;
 
 fn Foo() {
   returned var x: () = ();
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/returned/fail_returned_var_mismatch_signature.carbon:[[@LINE+1]]: return var; should not provide a return value, to match the function's signature.
+  // CHECK:STDERR: COMPILATION ERROR: 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/var/returned/fail_returned_var_multi_auto.carbon b/explorer/testdata/var/returned/fail_returned_var_multi_auto.carbon
index 493789b77346..02b9f0b74d7a 100644
--- a/explorer/testdata/var/returned/fail_returned_var_multi_auto.carbon
+++ b/explorer/testdata/var/returned/fail_returned_var_multi_auto.carbon
@@ -13,7 +13,7 @@ fn Foo(a: i32, b: i32) -> auto {
     return var;
   }
   ret = a - b;
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/returned/fail_returned_var_multi_auto.carbon:[[@LINE+1]]: Only one return is allowed in a function with an `auto` return type.
+  // CHECK:STDERR: COMPILATION ERROR: 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/var/returned/fail_returned_var_type_mismatch.carbon b/explorer/testdata/var/returned/fail_returned_var_type_mismatch.carbon
index ebf1b9bf7d46..fd4ac5b03d55 100644
--- a/explorer/testdata/var/returned/fail_returned_var_type_mismatch.carbon
+++ b/explorer/testdata/var/returned/fail_returned_var_type_mismatch.carbon
@@ -7,7 +7,7 @@
 package ExplorerTest api;
 
 fn AddInt(a: i32, b: i32) -> i32 {
-  // CHECK:STDERR: COMPILATION ERROR: explorer/testdata/var/returned/fail_returned_var_type_mismatch.carbon:[[@LINE+1]]: type of returned var `bool` does not match return type `i32`
+  // CHECK:STDERR: COMPILATION ERROR: 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/testing/file_test/BUILD b/testing/file_test/BUILD
index aed18a3adbe7..43615a82f7eb 100644
--- a/testing/file_test/BUILD
+++ b/testing/file_test/BUILD
@@ -19,7 +19,7 @@ cc_library(
 )
 
 file_test(
-    name = "file_test",
+    name = "file_test_base_test",
     srcs = ["file_test_base_test.cpp"],
     tests = ["example.carbon"],
     deps = [
diff --git a/testing/file_test/file_test_base.cpp b/testing/file_test/file_test_base.cpp
index 4b9645f5fbf1..9f06cb58530e 100644
--- a/testing/file_test/file_test_base.cpp
+++ b/testing/file_test/file_test_base.cpp
@@ -4,27 +4,49 @@
 
 #include "testing/file_test/file_test_base.h"
 
+#include <filesystem>
 #include <fstream>
 
 #include "common/check.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/InitLLVM.h"
 
-static std::string* subset_target = nullptr;
-
 namespace Carbon::Testing {
 
+// The length of the base directory.
+static int base_dir_len = 0;
+// The name of the `.subset` target.
+static std::string* subset_target = nullptr;
+// The original working directory for restoration after each test.
+static std::filesystem::path* orig_working_dir = nullptr;
+
 using ::testing::Eq;
 
+FileTestBase::FileTestBase(const std::filesystem::path& path) : path_(&path) {
+  // Run from the file's parent directory.
+  std::error_code ec;
+  std::filesystem::current_path(path.parent_path(), ec);
+  CARBON_CHECK(!ec) << ec.message();
+}
+
+FileTestBase::~FileTestBase() {
+  // Restore the original working directory.
+  std::error_code ec;
+  std::filesystem::current_path(*orig_working_dir, ec);
+  CARBON_CHECK(!ec) << ec.message();
+}
+
 void FileTestBase::RegisterTests(
-    const char* fixture_label, const std::vector<llvm::StringRef>& paths,
-    std::function<FileTestBase*(llvm::StringRef)> factory) {
+    const char* fixture_label, const std::vector<std::filesystem::path>& paths,
+    std::function<FileTestBase*(const std::filesystem::path&)> factory) {
   // Use RegisterTest instead of INSTANTIATE_TEST_CASE_P because of ordering
   // issues between container initialization and test instantiation by
   // InitGoogleTest.
-  for (auto path : paths) {
-    testing::RegisterTest(fixture_label, path.data(), nullptr, path.data(),
-                          __FILE__, __LINE__, [=]() { return factory(path); });
+  for (const auto& path : paths) {
+    std::string test_name = path.string().substr(base_dir_len);
+    testing::RegisterTest(fixture_label, test_name.c_str(), nullptr,
+                          test_name.c_str(), __FILE__, __LINE__,
+                          [=]() { return factory(path); });
   }
 }
 
@@ -48,7 +70,7 @@ auto FileTestBase::TestBody() -> void {
   // Load expected output.
   std::vector<testing::Matcher<std::string>> expected_stdout;
   std::vector<testing::Matcher<std::string>> expected_stderr;
-  std::ifstream file_content(path_.str());
+  std::ifstream file_content(path());
   int line_index = 0;
   std::string line_str;
   while (std::getline(file_content, line_str)) {
@@ -84,7 +106,8 @@ auto FileTestBase::TestBody() -> void {
   if (HasFailure()) {
     return;
   }
-  EXPECT_THAT(!filename().starts_with("fail_"), Eq(run_succeeded))
+  EXPECT_THAT(!llvm::StringRef(path().filename()).starts_with("fail_"),
+              Eq(run_succeeded))
       << "Tests should be prefixed with `fail_` if and only if running them "
          "is expected to fail.";
 
@@ -175,31 +198,8 @@ auto FileTestBase::TransformExpectation(int line_index, llvm::StringRef in)
   return testing::MatchesRegex(str);
 }
 
-auto FileTestBase::filename() -> llvm::StringRef {
-  auto last_slash = path_.rfind("/");
-  if (last_slash == llvm::StringRef::npos) {
-    return path_;
-  } else {
-    return path_.substr(last_slash + 1);
-  }
-}
-
 }  // namespace Carbon::Testing
 
-// Returns the name of the subset target.
-static auto GetSubsetTarget() -> std::string {
-  char* name = getenv("TEST_TARGET");
-  if (name == nullptr) {
-    return "<missing TEST_TARGET>";
-  }
-
-  if (llvm::StringRef(name).ends_with(".subset")) {
-    return name;
-  } else {
-    return std::string(name) + ".subset";
-  }
-}
-
 auto main(int argc, char** argv) -> int {
   testing::InitGoogleTest(&argc, argv);
   llvm::setBugReportMsg(
@@ -213,10 +213,42 @@ auto main(int argc, char** argv) -> int {
     return EXIT_FAILURE;
   }
 
-  std::string subset_target_storage = GetSubsetTarget();
-  ::subset_target = &subset_target_storage;
+  const char* target = getenv("TEST_TARGET");
+  CARBON_CHECK(target != nullptr);
 
-  std::vector<llvm::StringRef> paths(argv + 1, argv + argc);
+  // Configure the name of the subset target.
+  std::string subset_target_storage = target;
+  static constexpr char SubsetSuffix[] = ".subset";
+  if (!llvm::StringRef(subset_target_storage).ends_with(SubsetSuffix)) {
+    subset_target_storage += SubsetSuffix;
+  }
+  Carbon::Testing::subset_target = &subset_target_storage;
+
+  // Save the working directory for later restoration.
+  std::error_code ec;
+  std::filesystem::path orig_working_dir_storage =
+      std::filesystem::current_path(ec);
+  CARBON_CHECK(!ec) << ec.message();
+  Carbon::Testing::orig_working_dir = &orig_working_dir_storage;
+
+  // Configure the base directory for test names.
+  llvm::StringRef target_dir = target;
+  // Leaves one slash.
+  CARBON_CHECK(target_dir.consume_front("/"));
+  target_dir = target_dir.substr(0, target_dir.rfind(":"));
+  std::string base_dir =
+      orig_working_dir_storage.string() + target_dir.str() + "/";
+  Carbon::Testing::base_dir_len = base_dir.size();
+
+  // Register tests based on their absolute path.
+  std::vector<std::filesystem::path> paths;
+  for (int i = 1; i < argc; ++i) {
+    auto path = std::filesystem::absolute(argv[i], ec);
+    CARBON_CHECK(!ec) << argv[i] << ": " << ec.message();
+    CARBON_CHECK(llvm::StringRef(path.string()).starts_with(base_dir))
+        << "\n  " << path << "\n  should start with\n  " << base_dir;
+    paths.push_back(path);
+  }
   Carbon::Testing::RegisterFileTests(paths);
 
   return RUN_ALL_TESTS();
diff --git a/testing/file_test/file_test_base.h b/testing/file_test/file_test_base.h
index 7177504c7681..ee11b3221d6f 100644
--- a/testing/file_test/file_test_base.h
+++ b/testing/file_test/file_test_base.h
@@ -8,6 +8,7 @@
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
+#include <filesystem>
 #include <functional>
 #include <vector>
 
@@ -32,12 +33,14 @@ namespace Carbon::Testing {
 // `lit_autoupdate.py` automatically constructs compatible lines.
 class FileTestBase : public testing::Test {
  public:
-  explicit FileTestBase(const llvm::StringRef path) : path_(path) {}
+  explicit FileTestBase(const std::filesystem::path& path);
+  ~FileTestBase() override;
 
   // Used by children to register tests with gtest.
   static void RegisterTests(
-      const char* fixture_label, const std::vector<llvm::StringRef>& paths,
-      std::function<FileTestBase*(llvm::StringRef)> factory);
+      const char* fixture_label,
+      const std::vector<std::filesystem::path>& paths,
+      std::function<FileTestBase*(const std::filesystem::path&)> factory);
 
   // Implemented by children to run the test. Called by the TestBody
   // implementation, which will validate stdout and stderr. The return value
@@ -49,11 +52,8 @@ class FileTestBase : public testing::Test {
   // issues are a little easier to identify by the different line.
   auto TestBody() -> void final;
 
-  // Returns the filename of the file being tested.
-  auto filename() -> llvm::StringRef;
-
   // Returns the full path of the file being tested.
-  auto path() -> llvm::StringRef { return path_; };
+  auto path() -> const std::filesystem::path& { return *path_; };
 
  private:
   // Transforms an expectation on a given line from `FileCheck` syntax into a
@@ -61,11 +61,11 @@ class FileTestBase : public testing::Test {
   static auto TransformExpectation(int line_index, llvm::StringRef in)
       -> testing::Matcher<std::string>;
 
-  llvm::StringRef path_;
+  const std::filesystem::path* path_;
 };
 
 // Must be implemented by the individual file_test to initialize tests.
-extern auto RegisterFileTests(const std::vector<llvm::StringRef>& paths)
+extern auto RegisterFileTests(const std::vector<std::filesystem::path>& paths)
     -> void;
 
 }  // namespace Carbon::Testing
diff --git a/testing/file_test/file_test_base_test.cpp b/testing/file_test/file_test_base_test.cpp
index 51ff16a1b834..c44d097004cc 100644
--- a/testing/file_test/file_test_base_test.cpp
+++ b/testing/file_test/file_test_base_test.cpp
@@ -17,11 +17,13 @@ namespace {
 
 class FileTestBaseTest : public FileTestBase {
  public:
-  explicit FileTestBaseTest(llvm::StringRef path) : FileTestBase(path) {}
+  explicit FileTestBaseTest(const std::filesystem::path& path)
+      : FileTestBase(path) {}
 
   auto RunOverFile(llvm::raw_ostream& stdout, llvm::raw_ostream& stderr)
       -> bool override {
-    if (filename() == "example.carbon") {
+    auto filename = path().filename();
+    if (filename == "example.carbon") {
       stdout << "something\n"
                 "\n"
                 "8: Line delta\n"
@@ -29,11 +31,11 @@ class FileTestBaseTest : public FileTestBase {
                 "+*[]{}\n"
                 "Foo baz\n";
       return true;
-    } else if (filename() == "fail_example.carbon") {
+    } else if (filename == "fail_example.carbon") {
       stderr << "Oops\n";
       return false;
     } else {
-      ADD_FAILURE() << "Unexpected file: " << path().str();
+      ADD_FAILURE() << "Unexpected file: " << filename;
       return false;
     }
   }
@@ -41,10 +43,12 @@ class FileTestBaseTest : public FileTestBase {
 
 }  // namespace
 
-auto RegisterFileTests(const std::vector<llvm::StringRef>& paths) -> void {
-  FileTestBaseTest::RegisterTests(
-      "FileTestBaseTest", paths,
-      [](llvm::StringRef path) { return new FileTestBaseTest(path); });
+auto RegisterFileTests(const std::vector<std::filesystem::path>& paths)
+    -> void {
+  FileTestBaseTest::RegisterTests("FileTestBaseTest", paths,
+                                  [](const std::filesystem::path& path) {
+                                    return new FileTestBaseTest(path);
+                                  });
 }
 
 }  // namespace Carbon::Testing
diff --git a/testing/scripts/autoupdate_testdata_base.py b/testing/scripts/autoupdate_testdata_base.py
index 2e8fc8f8caaf..acd77b8ce104 100755
--- a/testing/scripts/autoupdate_testdata_base.py
+++ b/testing/scripts/autoupdate_testdata_base.py
@@ -87,7 +87,7 @@ def parse_args() -> ParsedArgs:
     parser.add_argument(
         "--line_number_pattern",
         metavar="PATTERN",
-        default=r"(?P<prefix>/(?P<filename>\w+\.carbon):)"
+        default=r"(?P<prefix>(?P<filename>\w+\.carbon):)"
         r"(?P<line>\d+)(?P<suffix>(?:\D|$))",
         help="A regular expression which matches line numbers to update as its "
         "only group. Capture groups 'prefix', 'line', and 'suffix' are "
@@ -304,13 +304,16 @@ def get_matchable_test_output(
     """Runs the autoupdate command and returns the output lines."""
     # Run the autoupdate command to generate output.
     # (`bazel run` would serialize)
-    autoupdate_cmd = TOOLS[tool].replace("//", "./bazel-bin/").replace(":", "/")
+    autoupdate_cmd = Path.cwd().joinpath(
+        TOOLS[tool].replace("//", "./bazel-bin/").replace(":", "/")
+    )
     p = subprocess.run(
-        [autoupdate_cmd] + autoupdate_args + [test],
+        [str(autoupdate_cmd)] + autoupdate_args + [Path(test).name],
         env={"LLVM_SYMBOLIZER_PATH": llvm_symbolizer},
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE,
         encoding="utf-8",
+        cwd=str(Path(test).parent),
     )
 
     out_lines = label_output("STDOUT:", p.stdout)
@@ -324,10 +327,7 @@ def get_matchable_test_output(
             # `lit` uses full paths to the test file, so use a regex to ignore
             # paths when used.
             line = line.replace(test, f"{{{{.*}}}}/{test}")
-            line = bazel_runfiles.sub("{{.*}}/", line)
-        else:
-            # When not using `lit`, the runfiles path is removed.
-            line = bazel_runfiles.sub("", line)
+        line = bazel_runfiles.sub("{{.*}}/", line)
 
         for line_matcher, before, after in extra_check_replacements:
             if line_matcher.match(line):
diff --git a/toolchain/lexer/lexer_file_test.cpp b/toolchain/lexer/lexer_file_test.cpp
index a9c0222c83d0..0776c3a064e9 100644
--- a/toolchain/lexer/lexer_file_test.cpp
+++ b/toolchain/lexer/lexer_file_test.cpp
@@ -17,21 +17,25 @@ namespace {
 
 class LexerFileTest : public FileTestBase {
  public:
-  explicit LexerFileTest(llvm::StringRef path) : FileTestBase(path) {}
+  explicit LexerFileTest(const std::filesystem::path& path)
+      : FileTestBase(path) {}
 
   auto RunOverFile(llvm::raw_ostream& stdout, llvm::raw_ostream& stderr)
       -> bool override {
     Driver driver(stdout, stderr);
-    return driver.RunFullCommand({"dump", "tokens", path()});
+    return driver.RunFullCommand(
+        {"dump", "tokens", path().filename().string()});
   }
 };
 
 }  // namespace
 
-auto RegisterFileTests(const std::vector<llvm::StringRef>& paths) -> void {
-  LexerFileTest::RegisterTests(
-      "LexerFileTest", paths,
-      [](llvm::StringRef path) { return new LexerFileTest(path); });
+auto RegisterFileTests(const std::vector<std::filesystem::path>& paths)
+    -> void {
+  LexerFileTest::RegisterTests("LexerFileTest", paths,
+                               [](const std::filesystem::path& path) {
+                                 return new LexerFileTest(path);
+                               });
 }
 
 }  // namespace Carbon::Testing
diff --git a/toolchain/lowering/lowering_file_test.cpp b/toolchain/lowering/lowering_file_test.cpp
index 6114cfd545ad..d0f8858c8ba6 100644
--- a/toolchain/lowering/lowering_file_test.cpp
+++ b/toolchain/lowering/lowering_file_test.cpp
@@ -17,21 +17,25 @@ namespace {
 
 class LoweringFileTest : public FileTestBase {
  public:
-  explicit LoweringFileTest(llvm::StringRef path) : FileTestBase(path) {}
+  explicit LoweringFileTest(const std::filesystem::path& path)
+      : FileTestBase(path) {}
 
   auto RunOverFile(llvm::raw_ostream& stdout, llvm::raw_ostream& stderr)
       -> bool override {
     Driver driver(stdout, stderr);
-    return driver.RunFullCommand({"dump", "llvm-ir", path()});
+    return driver.RunFullCommand(
+        {"dump", "llvm-ir", path().filename().string()});
   }
 };
 
 }  // namespace
 
-auto RegisterFileTests(const std::vector<llvm::StringRef>& paths) -> void {
-  LoweringFileTest::RegisterTests(
-      "LoweringFileTest", paths,
-      [](llvm::StringRef path) { return new LoweringFileTest(path); });
+auto RegisterFileTests(const std::vector<std::filesystem::path>& paths)
+    -> void {
+  LoweringFileTest::RegisterTests("LoweringFileTest", paths,
+                                  [=](const std::filesystem::path& path) {
+                                    return new LoweringFileTest(path);
+                                  });
 }
 
 }  // namespace Carbon::Testing
diff --git a/toolchain/lowering/testdata/basics/empty.carbon b/toolchain/lowering/testdata/basics/empty.carbon
index 2e594955c003..de1e267a2214 100644
--- a/toolchain/lowering/testdata/basics/empty.carbon
+++ b/toolchain/lowering/testdata/basics/empty.carbon
@@ -3,5 +3,5 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/basics/empty.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/basics/empty.carbon"
+// CHECK:STDOUT: ; ModuleID = 'empty.carbon'
+// CHECK:STDOUT: source_filename = "empty.carbon"
diff --git a/toolchain/lowering/testdata/basics/fail_before_lowering.carbon b/toolchain/lowering/testdata/basics/fail_before_lowering.carbon
index 6adaaf683e53..637d4f5c801c 100644
--- a/toolchain/lowering/testdata/basics/fail_before_lowering.carbon
+++ b/toolchain/lowering/testdata/basics/fail_before_lowering.carbon
@@ -5,5 +5,5 @@
 // This validates that earlier errors prevent lowering, without crashing.
 // AUTOUPDATE
 
-// CHECK:STDERR: toolchain/lowering/testdata/basics/fail_before_lowering.carbon:[[@LINE+1]]:1: Unrecognized declaration introducer.
+// CHECK:STDERR: fail_before_lowering.carbon:[[@LINE+1]]:1: Unrecognized declaration introducer.
 a;
diff --git a/toolchain/lowering/testdata/basics/zero.carbon b/toolchain/lowering/testdata/basics/zero.carbon
index 9f0081a4498f..71b8f654fab7 100644
--- a/toolchain/lowering/testdata/basics/zero.carbon
+++ b/toolchain/lowering/testdata/basics/zero.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/basics/zero.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/basics/zero.carbon"
+// CHECK:STDOUT: ; ModuleID = 'zero.carbon'
+// CHECK:STDOUT: source_filename = "zero.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: define i32 @Main() {
 // CHECK:STDOUT: entry:
diff --git a/toolchain/lowering/testdata/function/definition/params_one.carbon b/toolchain/lowering/testdata/function/definition/params_one.carbon
index a3ed4233f9e0..052a18826335 100644
--- a/toolchain/lowering/testdata/function/definition/params_one.carbon
+++ b/toolchain/lowering/testdata/function/definition/params_one.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/function/definition/params_one.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/function/definition/params_one.carbon"
+// CHECK:STDOUT: ; ModuleID = 'params_one.carbon'
+// CHECK:STDOUT: source_filename = "params_one.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: %0 = type {}
 // CHECK:STDOUT:
diff --git a/toolchain/lowering/testdata/function/definition/params_two.carbon b/toolchain/lowering/testdata/function/definition/params_two.carbon
index f284c112e7da..93c679046d15 100644
--- a/toolchain/lowering/testdata/function/definition/params_two.carbon
+++ b/toolchain/lowering/testdata/function/definition/params_two.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/function/definition/params_two.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/function/definition/params_two.carbon"
+// CHECK:STDOUT: ; ModuleID = 'params_two.carbon'
+// CHECK:STDOUT: source_filename = "params_two.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: %0 = type {}
 // CHECK:STDOUT:
diff --git a/toolchain/lowering/testdata/function/definition/params_zero.carbon b/toolchain/lowering/testdata/function/definition/params_zero.carbon
index dbc40f376e2a..7e4f4410f0fe 100644
--- a/toolchain/lowering/testdata/function/definition/params_zero.carbon
+++ b/toolchain/lowering/testdata/function/definition/params_zero.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/function/definition/params_zero.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/function/definition/params_zero.carbon"
+// CHECK:STDOUT: ; ModuleID = 'params_zero.carbon'
+// CHECK:STDOUT: source_filename = "params_zero.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: %0 = type {}
 // CHECK:STDOUT:
diff --git a/toolchain/lowering/testdata/return/no_value.carbon b/toolchain/lowering/testdata/return/no_value.carbon
index e5be729f8565..04dd913d1878 100644
--- a/toolchain/lowering/testdata/return/no_value.carbon
+++ b/toolchain/lowering/testdata/return/no_value.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/return/no_value.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/return/no_value.carbon"
+// CHECK:STDOUT: ; ModuleID = 'no_value.carbon'
+// CHECK:STDOUT: source_filename = "no_value.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: %0 = type {}
 // CHECK:STDOUT:
diff --git a/toolchain/lowering/testdata/return/value.carbon b/toolchain/lowering/testdata/return/value.carbon
index acf9ee2cf2c9..41602f972ac1 100644
--- a/toolchain/lowering/testdata/return/value.carbon
+++ b/toolchain/lowering/testdata/return/value.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/return/value.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/return/value.carbon"
+// CHECK:STDOUT: ; ModuleID = 'value.carbon'
+// CHECK:STDOUT: source_filename = "value.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: define i32 @Main() {
 // CHECK:STDOUT: entry:
diff --git a/toolchain/lowering/testdata/struct/empty.carbon b/toolchain/lowering/testdata/struct/empty.carbon
index 303234ecd4f9..9e44020d6cd1 100644
--- a/toolchain/lowering/testdata/struct/empty.carbon
+++ b/toolchain/lowering/testdata/struct/empty.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/struct/empty.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/struct/empty.carbon"
+// CHECK:STDOUT: ; ModuleID = 'empty.carbon'
+// CHECK:STDOUT: source_filename = "empty.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: %0 = type {}
 // CHECK:STDOUT:
diff --git a/toolchain/lowering/testdata/struct/member_access.carbon b/toolchain/lowering/testdata/struct/member_access.carbon
index 855e6199f4a6..ec52543a351d 100644
--- a/toolchain/lowering/testdata/struct/member_access.carbon
+++ b/toolchain/lowering/testdata/struct/member_access.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/struct/member_access.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/struct/member_access.carbon"
+// CHECK:STDOUT: ; ModuleID = 'member_access.carbon'
+// CHECK:STDOUT: source_filename = "member_access.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: %0 = type { double, i32 }
 // CHECK:STDOUT: %1 = type { double, i32 }
diff --git a/toolchain/lowering/testdata/struct/one_entry.carbon b/toolchain/lowering/testdata/struct/one_entry.carbon
index 85e57b14a46a..bf0358681ef0 100644
--- a/toolchain/lowering/testdata/struct/one_entry.carbon
+++ b/toolchain/lowering/testdata/struct/one_entry.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/struct/one_entry.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/struct/one_entry.carbon"
+// CHECK:STDOUT: ; ModuleID = 'one_entry.carbon'
+// CHECK:STDOUT: source_filename = "one_entry.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: %0 = type { i32 }
 // CHECK:STDOUT: %1 = type { i32 }
diff --git a/toolchain/lowering/testdata/struct/two_entries.carbon b/toolchain/lowering/testdata/struct/two_entries.carbon
index 45b1f2664a33..9deb4e155507 100644
--- a/toolchain/lowering/testdata/struct/two_entries.carbon
+++ b/toolchain/lowering/testdata/struct/two_entries.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/struct/two_entries.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/struct/two_entries.carbon"
+// CHECK:STDOUT: ; ModuleID = 'two_entries.carbon'
+// CHECK:STDOUT: source_filename = "two_entries.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: %0 = type { i32, i32 }
 // CHECK:STDOUT: %1 = type { i32, i32 }
diff --git a/toolchain/lowering/testdata/var/local.carbon b/toolchain/lowering/testdata/var/local.carbon
index f9a4767da0f7..4e58b671bfb7 100644
--- a/toolchain/lowering/testdata/var/local.carbon
+++ b/toolchain/lowering/testdata/var/local.carbon
@@ -3,8 +3,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: ; ModuleID = 'toolchain/lowering/testdata/var/local.carbon'
-// CHECK:STDOUT: source_filename = "toolchain/lowering/testdata/var/local.carbon"
+// CHECK:STDOUT: ; ModuleID = 'local.carbon'
+// CHECK:STDOUT: source_filename = "local.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: define i32 @Run() {
 // CHECK:STDOUT: entry:
diff --git a/toolchain/parser/parse_tree_file_test.cpp b/toolchain/parser/parse_tree_file_test.cpp
index 6a7b5bead424..bea908733fdd 100644
--- a/toolchain/parser/parse_tree_file_test.cpp
+++ b/toolchain/parser/parse_tree_file_test.cpp
@@ -17,21 +17,25 @@ namespace {
 
 class ParserFileTest : public FileTestBase {
  public:
-  explicit ParserFileTest(llvm::StringRef path) : FileTestBase(path) {}
+  explicit ParserFileTest(const std::filesystem::path& path)
+      : FileTestBase(path) {}
 
   auto RunOverFile(llvm::raw_ostream& stdout, llvm::raw_ostream& stderr)
       -> bool override {
     Driver driver(stdout, stderr);
-    return driver.RunFullCommand({"dump", "parse-tree", path()});
+    return driver.RunFullCommand(
+        {"dump", "parse-tree", path().filename().string()});
   }
 };
 
 }  // namespace
 
-auto RegisterFileTests(const std::vector<llvm::StringRef>& paths) -> void {
-  ParserFileTest::RegisterTests(
-      "ParserFileTest", paths,
-      [](llvm::StringRef path) { return new ParserFileTest(path); });
+auto RegisterFileTests(const std::vector<std::filesystem::path>& paths)
+    -> void {
+  ParserFileTest::RegisterTests("ParserFileTest", paths,
+                                [](const std::filesystem::path& path) {
+                                  return new ParserFileTest(path);
+                                });
 }
 
 }  // namespace Carbon::Testing
diff --git a/toolchain/parser/testdata/basics/fail_invalid_designators.carbon b/toolchain/parser/testdata/basics/fail_invalid_designators.carbon
index 3b94970ff0fa..3f6cd4146f8c 100644
--- a/toolchain/parser/testdata/basics/fail_invalid_designators.carbon
+++ b/toolchain/parser/testdata/basics/fail_invalid_designators.carbon
@@ -27,10 +27,10 @@
 
 // NOTE: Move to its own directory when more tests are added.
 fn F() {
-  // CHECK:STDERR: toolchain/parser/testdata/basics/fail_invalid_designators.carbon:[[@LINE+1]]:5: Expected identifier after `.`.
+  // CHECK:STDERR: fail_invalid_designators.carbon:[[@LINE+1]]:5: Expected identifier after `.`.
   a.;
-  // CHECK:STDERR: toolchain/parser/testdata/basics/fail_invalid_designators.carbon:[[@LINE+1]]:5: Expected identifier after `.`.
+  // CHECK:STDERR: fail_invalid_designators.carbon:[[@LINE+1]]:5: Expected identifier after `.`.
   a.fn;
-  // CHECK:STDERR: toolchain/parser/testdata/basics/fail_invalid_designators.carbon:[[@LINE+1]]:5: Expected identifier after `.`.
+  // CHECK:STDERR: fail_invalid_designators.carbon:[[@LINE+1]]:5: Expected identifier after `.`.
   a.42;
 }
diff --git a/toolchain/parser/testdata/basics/fail_no_intro_with_semi.carbon b/toolchain/parser/testdata/basics/fail_no_intro_with_semi.carbon
index 8f36f4ec14a5..b0739fa40f96 100644
--- a/toolchain/parser/testdata/basics/fail_no_intro_with_semi.carbon
+++ b/toolchain/parser/testdata/basics/fail_no_intro_with_semi.carbon
@@ -8,5 +8,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/basics/fail_no_intro_with_semi.carbon:[[@LINE+1]]:1: Unrecognized declaration introducer.
+// CHECK:STDERR: fail_no_intro_with_semi.carbon:[[@LINE+1]]:1: Unrecognized declaration introducer.
 foo;
diff --git a/toolchain/parser/testdata/basics/fail_no_intro_without_semi.carbon b/toolchain/parser/testdata/basics/fail_no_intro_without_semi.carbon
index f1f2041f3cd5..a75c063379eb 100644
--- a/toolchain/parser/testdata/basics/fail_no_intro_without_semi.carbon
+++ b/toolchain/parser/testdata/basics/fail_no_intro_without_semi.carbon
@@ -8,5 +8,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/basics/fail_no_intro_without_semi.carbon:[[@LINE+1]]:1: Unrecognized declaration introducer.
+// CHECK:STDERR: fail_no_intro_without_semi.carbon:[[@LINE+1]]:1: Unrecognized declaration introducer.
 foo bar baz
diff --git a/toolchain/parser/testdata/basics/fail_paren_match_regression.carbon b/toolchain/parser/testdata/basics/fail_paren_match_regression.carbon
index 393cb37bf8f0..2d6371e2a496 100644
--- a/toolchain/parser/testdata/basics/fail_paren_match_regression.carbon
+++ b/toolchain/parser/testdata/basics/fail_paren_match_regression.carbon
@@ -16,7 +16,7 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/basics/fail_paren_match_regression.carbon:[[@LINE+3]]:5: Expected pattern in `var` declaration.
-// CHECK:STDERR: toolchain/parser/testdata/basics/fail_paren_match_regression.carbon:[[@LINE+2]]:12: Expected `,` or `)`.
-// CHECK:STDERR: toolchain/parser/testdata/basics/fail_paren_match_regression.carbon:[[@LINE+1]]:15: Expected `;` after expression.
+// CHECK:STDERR: fail_paren_match_regression.carbon:[[@LINE+3]]:5: Expected pattern in `var` declaration.
+// CHECK:STDERR: fail_paren_match_regression.carbon:[[@LINE+2]]:12: Expected `,` or `)`.
+// CHECK:STDERR: fail_paren_match_regression.carbon:[[@LINE+1]]:15: Expected `;` after expression.
 var = (foo {})
diff --git a/toolchain/parser/testdata/for/fail_colon_instead_of_in.carbon b/toolchain/parser/testdata/for/fail_colon_instead_of_in.carbon
index b3267f1dd1a9..ee651e69d6ed 100644
--- a/toolchain/parser/testdata/for/fail_colon_instead_of_in.carbon
+++ b/toolchain/parser/testdata/for/fail_colon_instead_of_in.carbon
@@ -30,7 +30,7 @@
 // CHECK:STDOUT: ]
 
 fn foo() {
-  // CHECK:STDERR: toolchain/parser/testdata/for/fail_colon_instead_of_in.carbon:[[@LINE+1]]:19: `:` should be replaced by `in`.
+  // CHECK:STDERR: fail_colon_instead_of_in.carbon:[[@LINE+1]]:19: `:` should be replaced by `in`.
   for (var x: i32 : y) {
     Print(x);
   }
diff --git a/toolchain/parser/testdata/for/fail_missing_in.carbon b/toolchain/parser/testdata/for/fail_missing_in.carbon
index df12479eac60..d61bc4576ba0 100644
--- a/toolchain/parser/testdata/for/fail_missing_in.carbon
+++ b/toolchain/parser/testdata/for/fail_missing_in.carbon
@@ -30,7 +30,7 @@
 // CHECK:STDOUT: ]
 
 fn foo() {
-  // CHECK:STDERR: toolchain/parser/testdata/for/fail_missing_in.carbon:[[@LINE+1]]:19: Expected `in` after loop `var` declaration.
+  // CHECK:STDERR: fail_missing_in.carbon:[[@LINE+1]]:19: Expected `in` after loop `var` declaration.
   for (var x: i32 y) {
     Print(x);
   }
diff --git a/toolchain/parser/testdata/for/fail_missing_var.carbon b/toolchain/parser/testdata/for/fail_missing_var.carbon
index 8fdee45daa0b..da5e6de8973c 100644
--- a/toolchain/parser/testdata/for/fail_missing_var.carbon
+++ b/toolchain/parser/testdata/for/fail_missing_var.carbon
@@ -25,7 +25,7 @@
 // CHECK:STDOUT: ]
 
 fn foo() {
-  // CHECK:STDERR: toolchain/parser/testdata/for/fail_missing_var.carbon:[[@LINE+1]]:8: Expected `var` declaration.
+  // CHECK:STDERR: fail_missing_var.carbon:[[@LINE+1]]:8: Expected `var` declaration.
   for (x: i32 in y) {
     Print(x);
   }
diff --git a/toolchain/parser/testdata/function/declaration/fail_identifier_instead_of_sig.carbon b/toolchain/parser/testdata/function/declaration/fail_identifier_instead_of_sig.carbon
index 99b273b0c5b4..90a686964079 100644
--- a/toolchain/parser/testdata/function/declaration/fail_identifier_instead_of_sig.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_identifier_instead_of_sig.carbon
@@ -10,5 +10,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_identifier_instead_of_sig.carbon:[[@LINE+1]]:8: `fn` requires a `(` for parameters.
+// CHECK:STDERR: fail_identifier_instead_of_sig.carbon:[[@LINE+1]]:8: `fn` requires a `(` for parameters.
 fn foo bar;
diff --git a/toolchain/parser/testdata/function/declaration/fail_missing_deduced_close.carbon b/toolchain/parser/testdata/function/declaration/fail_missing_deduced_close.carbon
index 5b2dfae3a74e..b36596349f50 100644
--- a/toolchain/parser/testdata/function/declaration/fail_missing_deduced_close.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_missing_deduced_close.carbon
@@ -16,7 +16,7 @@
 // CHECK:STDOUT: ]
 
 // Fix and uncomment this to test error handling.
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_missing_deduced_close.carbon:[[@LINE+2]]:7: Closing symbol does not match most recent opening symbol.
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_missing_deduced_close.carbon:[[@LINE+1]]:8: Expected parameter declaration.
+// CHECK:STDERR: fail_missing_deduced_close.carbon:[[@LINE+2]]:7: Closing symbol does not match most recent opening symbol.
+// CHECK:STDERR: fail_missing_deduced_close.carbon:[[@LINE+1]]:8: Expected parameter declaration.
 fn Div[();
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_missing_deduced_close.carbon:[[@LINE+0]]:174: A `(` for parameters is required after deduced parameters.
+// CHECK:STDERR: fail_missing_deduced_close.carbon:[[@LINE+0]]:127: A `(` for parameters is required after deduced parameters.
diff --git a/toolchain/parser/testdata/function/declaration/fail_missing_name.carbon b/toolchain/parser/testdata/function/declaration/fail_missing_name.carbon
index 7a5c95ba3de8..b4b4db89b7ff 100644
--- a/toolchain/parser/testdata/function/declaration/fail_missing_name.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_missing_name.carbon
@@ -9,5 +9,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_missing_name.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
+// CHECK:STDERR: fail_missing_name.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
 fn ();
diff --git a/toolchain/parser/testdata/function/declaration/fail_no_sig_or_semi.carbon b/toolchain/parser/testdata/function/declaration/fail_no_sig_or_semi.carbon
index ad0fc20ddf0f..151f5c225f38 100644
--- a/toolchain/parser/testdata/function/declaration/fail_no_sig_or_semi.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_no_sig_or_semi.carbon
@@ -10,5 +10,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_no_sig_or_semi.carbon:[[@LINE+1]]:7: `fn` requires a `(` for parameters.
+// CHECK:STDERR: fail_no_sig_or_semi.carbon:[[@LINE+1]]:7: `fn` requires a `(` for parameters.
 fn foo
diff --git a/toolchain/parser/testdata/function/declaration/fail_only_fn_and_semi.carbon b/toolchain/parser/testdata/function/declaration/fail_only_fn_and_semi.carbon
index 589592765a4c..49f693568ef9 100644
--- a/toolchain/parser/testdata/function/declaration/fail_only_fn_and_semi.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_only_fn_and_semi.carbon
@@ -9,5 +9,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_only_fn_and_semi.carbon:[[@LINE+1]]:3: `fn` introducer should be followed by a name.
+// CHECK:STDERR: fail_only_fn_and_semi.carbon:[[@LINE+1]]:3: `fn` introducer should be followed by a name.
 fn;
diff --git a/toolchain/parser/testdata/function/declaration/fail_repeated_fn_and_semi.carbon b/toolchain/parser/testdata/function/declaration/fail_repeated_fn_and_semi.carbon
index aee502fca0eb..f7d14d9301dc 100644
--- a/toolchain/parser/testdata/function/declaration/fail_repeated_fn_and_semi.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_repeated_fn_and_semi.carbon
@@ -9,5 +9,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_repeated_fn_and_semi.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
+// CHECK:STDERR: fail_repeated_fn_and_semi.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
 fn fn;
diff --git a/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_until_outdent.carbon b/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_until_outdent.carbon
index 524740f22fbb..2ed716690574 100644
--- a/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_until_outdent.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_until_outdent.carbon
@@ -14,7 +14,7 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-  // CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_until_outdent.carbon:[[@LINE+1]]:6: `fn` introducer should be followed by a name.
+  // CHECK:STDERR: fail_skip_indented_newline_until_outdent.carbon:[[@LINE+1]]:6: `fn` introducer should be followed by a name.
   fn (x,
       y,
       z)
diff --git a/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_with_semi.carbon b/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_with_semi.carbon
index 6e364daa9a22..cf5dc2a34a45 100644
--- a/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_with_semi.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_with_semi.carbon
@@ -14,7 +14,7 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_with_semi.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
+// CHECK:STDERR: fail_skip_indented_newline_with_semi.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
 fn (x,
     y,
     z);
diff --git a/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_without_semi.carbon b/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_without_semi.carbon
index 5cfaefedcccf..2c9f89c82535 100644
--- a/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_without_semi.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_without_semi.carbon
@@ -14,7 +14,7 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_skip_indented_newline_without_semi.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
+// CHECK:STDERR: fail_skip_indented_newline_without_semi.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
 fn (x,
     y,
     z)
diff --git a/toolchain/parser/testdata/function/declaration/fail_skip_to_newline_without_semi.carbon b/toolchain/parser/testdata/function/declaration/fail_skip_to_newline_without_semi.carbon
index 3e9ee853e2bd..394c3379e4cc 100644
--- a/toolchain/parser/testdata/function/declaration/fail_skip_to_newline_without_semi.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_skip_to_newline_without_semi.carbon
@@ -14,6 +14,6 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_skip_to_newline_without_semi.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
+// CHECK:STDERR: fail_skip_to_newline_without_semi.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
 fn ()
 fn F();
diff --git a/toolchain/parser/testdata/function/declaration/fail_skip_without_semi_to_curly.carbon b/toolchain/parser/testdata/function/declaration/fail_skip_without_semi_to_curly.carbon
index 4768473ca7dd..92ab55174df6 100644
--- a/toolchain/parser/testdata/function/declaration/fail_skip_without_semi_to_curly.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_skip_without_semi_to_curly.carbon
@@ -13,6 +13,6 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_skip_without_semi_to_curly.carbon:[[@LINE+1]]:1: Unrecognized declaration introducer.
+// CHECK:STDERR: fail_skip_without_semi_to_curly.carbon:[[@LINE+1]]:1: Unrecognized declaration introducer.
 struct X { fn () }
 fn F();
diff --git a/toolchain/parser/testdata/function/declaration/fail_with_identifier_as_param.carbon b/toolchain/parser/testdata/function/declaration/fail_with_identifier_as_param.carbon
index cff7b9b889cb..c76e03393099 100644
--- a/toolchain/parser/testdata/function/declaration/fail_with_identifier_as_param.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_with_identifier_as_param.carbon
@@ -15,5 +15,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_with_identifier_as_param.carbon:[[@LINE+1]]:11: Expected parameter declaration.
+// CHECK:STDERR: fail_with_identifier_as_param.carbon:[[@LINE+1]]:11: Expected parameter declaration.
 fn foo(bar);
diff --git a/toolchain/parser/testdata/function/declaration/fail_without_name_and_many_tokens_in_params.carbon b/toolchain/parser/testdata/function/declaration/fail_without_name_and_many_tokens_in_params.carbon
index 3ed38586e280..e991f568f3b3 100644
--- a/toolchain/parser/testdata/function/declaration/fail_without_name_and_many_tokens_in_params.carbon
+++ b/toolchain/parser/testdata/function/declaration/fail_without_name_and_many_tokens_in_params.carbon
@@ -9,5 +9,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/function/declaration/fail_without_name_and_many_tokens_in_params.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
+// CHECK:STDERR: fail_without_name_and_many_tokens_in_params.carbon:[[@LINE+1]]:4: `fn` introducer should be followed by a name.
 fn (a tokens c d e f g h i j k l m n o p q r s t u v w x y z);
diff --git a/toolchain/parser/testdata/function/definition/fail_identifier_in_statements.carbon b/toolchain/parser/testdata/function/definition/fail_identifier_in_statements.carbon
index 40c1594917d0..4d8ea53b05f4 100644
--- a/toolchain/parser/testdata/function/definition/fail_identifier_in_statements.carbon
+++ b/toolchain/parser/testdata/function/definition/fail_identifier_in_statements.carbon
@@ -18,5 +18,5 @@ fn F() {
   // Note: this might become valid depending on the expression syntax. This test
   // shouldn't be taken as a sign it should remain invalid.
   bar
-// CHECK:STDERR: toolchain/parser/testdata/function/definition/fail_identifier_in_statements.carbon:[[@LINE+1]]:1: Expected `;` after expression.
+// CHECK:STDERR: fail_identifier_in_statements.carbon:[[@LINE+1]]:1: Expected `;` after expression.
 }
diff --git a/toolchain/parser/testdata/generics/deduced_params/fail_no_parens.carbon b/toolchain/parser/testdata/generics/deduced_params/fail_no_parens.carbon
index b6a776ba7738..b3203a01132c 100644
--- a/toolchain/parser/testdata/generics/deduced_params/fail_no_parens.carbon
+++ b/toolchain/parser/testdata/generics/deduced_params/fail_no_parens.carbon
@@ -33,14 +33,14 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/generics/deduced_params/fail_no_parens.carbon:[[@LINE+1]]:12: A `(` for parameters is required after deduced parameters.
+// CHECK:STDERR: fail_no_parens.carbon:[[@LINE+1]]:12: A `(` for parameters is required after deduced parameters.
 class Foo[];
 
-// CHECK:STDERR: toolchain/parser/testdata/generics/deduced_params/fail_no_parens.carbon:[[@LINE+1]]:18: A `(` for parameters is required after deduced parameters.
+// CHECK:STDERR: fail_no_parens.carbon:[[@LINE+1]]:18: A `(` for parameters is required after deduced parameters.
 class Foo[a: i32];
 
-// CHECK:STDERR: toolchain/parser/testdata/generics/deduced_params/fail_no_parens.carbon:[[@LINE+1]]:17: A `(` for parameters is required after deduced parameters.
+// CHECK:STDERR: fail_no_parens.carbon:[[@LINE+1]]:17: A `(` for parameters is required after deduced parameters.
 interface Bar[] {}
 
-// CHECK:STDERR: toolchain/parser/testdata/generics/deduced_params/fail_no_parens.carbon:[[@LINE+1]]:23: A `(` for parameters is required after deduced parameters.
+// CHECK:STDERR: fail_no_parens.carbon:[[@LINE+1]]:23: A `(` for parameters is required after deduced parameters.
 interface Bar[a: i32] {}
diff --git a/toolchain/parser/testdata/generics/interface/fail_missing_name.carbon b/toolchain/parser/testdata/generics/interface/fail_missing_name.carbon
index 26189e15fb4d..3b6536aacbe4 100644
--- a/toolchain/parser/testdata/generics/interface/fail_missing_name.carbon
+++ b/toolchain/parser/testdata/generics/interface/fail_missing_name.carbon
@@ -9,6 +9,6 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/generics/interface/fail_missing_name.carbon:[[@LINE+1]]:11: `interface` introducer should be followed by a name.
+// CHECK:STDERR: fail_missing_name.carbon:[[@LINE+1]]:11: `interface` introducer should be followed by a name.
 interface {
 }
diff --git a/toolchain/parser/testdata/generics/interface/fail_missing_open_curly.carbon b/toolchain/parser/testdata/generics/interface/fail_missing_open_curly.carbon
index 730d64c84eb1..57a361194b3c 100644
--- a/toolchain/parser/testdata/generics/interface/fail_missing_open_curly.carbon
+++ b/toolchain/parser/testdata/generics/interface/fail_missing_open_curly.carbon
@@ -13,8 +13,8 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/generics/interface/fail_missing_open_curly.carbon:[[@LINE+1]]:15: `interface` should either end with a `;` for a declaration or have a `{ ... }` block for a definition.
+// CHECK:STDERR: fail_missing_open_curly.carbon:[[@LINE+1]]:15: `interface` should either end with a `;` for a declaration or have a `{ ... }` block for a definition.
 interface Bar Baz {}
 
-// CHECK:STDERR: toolchain/parser/testdata/generics/interface/fail_missing_open_curly.carbon:[[@LINE+1]]:14: `interface` should either end with a `;` for a declaration or have a `{ ... }` block for a definition.
+// CHECK:STDERR: fail_missing_open_curly.carbon:[[@LINE+1]]:14: `interface` should either end with a `;` for a declaration or have a `{ ... }` block for a definition.
 interface Foo
diff --git a/toolchain/parser/testdata/generics/interface/fail_no_impl_allowed.carbon b/toolchain/parser/testdata/generics/interface/fail_no_impl_allowed.carbon
index fa4b8960a055..9eab49f8586a 100644
--- a/toolchain/parser/testdata/generics/interface/fail_no_impl_allowed.carbon
+++ b/toolchain/parser/testdata/generics/interface/fail_no_impl_allowed.carbon
@@ -27,7 +27,7 @@
 // CHECK:STDOUT: ]
 
 interface Foo {
-  // CHECK:STDERR: toolchain/parser/testdata/generics/interface/fail_no_impl_allowed.carbon:[[@LINE+1]]:39: Method implementations are not allowed in interfaces.
+  // CHECK:STDERR: fail_no_impl_allowed.carbon:[[@LINE+1]]:39: Method implementations are not allowed in interfaces.
   fn Add[self: Self](b: Self) -> Self {
     print("You can't do that.");
   }
diff --git a/toolchain/parser/testdata/generics/interface/fail_self_param_syntax.carbon b/toolchain/parser/testdata/generics/interface/fail_self_param_syntax.carbon
index adcce72bc124..2a745620c290 100644
--- a/toolchain/parser/testdata/generics/interface/fail_self_param_syntax.carbon
+++ b/toolchain/parser/testdata/generics/interface/fail_self_param_syntax.carbon
@@ -42,9 +42,9 @@
 // CHECK:STDOUT: ]
 
 interface Foo {
-  // CHECK:STDERR: toolchain/parser/testdata/generics/interface/fail_self_param_syntax.carbon:[[@LINE+1]]:13: Expected parameter declaration.
+  // CHECK:STDERR: fail_self_param_syntax.carbon:[[@LINE+1]]:13: Expected parameter declaration.
   fn Sub[me Self](b: Self) -> Self;
 
-  // CHECK:STDERR: toolchain/parser/testdata/generics/interface/fail_self_param_syntax.carbon:[[@LINE+1]]:10: Expected parameter declaration.
+  // CHECK:STDERR: fail_self_param_syntax.carbon:[[@LINE+1]]:10: Expected parameter declaration.
   fn Mul[Self](b: Self) -> Self;
 }
diff --git a/toolchain/parser/testdata/generics/named_constraint/fail_no_impl_allowed.carbon b/toolchain/parser/testdata/generics/named_constraint/fail_no_impl_allowed.carbon
index 83173b0332a9..8113343dcc37 100644
--- a/toolchain/parser/testdata/generics/named_constraint/fail_no_impl_allowed.carbon
+++ b/toolchain/parser/testdata/generics/named_constraint/fail_no_impl_allowed.carbon
@@ -27,6 +27,6 @@
 // CHECK:STDOUT: ]
 
 constraint Foo {
-  // CHECK:STDERR: toolchain/parser/testdata/generics/named_constraint/fail_no_impl_allowed.carbon:[[@LINE+1]]:39: Method implementations are not allowed in interfaces.
+  // CHECK:STDERR: fail_no_impl_allowed.carbon:[[@LINE+1]]:39: Method implementations are not allowed in interfaces.
   fn Add[self: Self](b: Self) -> Self {}
 }
diff --git a/toolchain/parser/testdata/if/fail_else_unbraced.carbon b/toolchain/parser/testdata/if/fail_else_unbraced.carbon
index c2c649636272..12f45b9bd0ab 100644
--- a/toolchain/parser/testdata/if/fail_else_unbraced.carbon
+++ b/toolchain/parser/testdata/if/fail_else_unbraced.carbon
@@ -61,15 +61,15 @@
 
 fn F() {
   if (a)
-    // CHECK:STDERR: toolchain/parser/testdata/if/fail_else_unbraced.carbon:[[@LINE+1]]:5: Expected braced code block.
+    // CHECK:STDERR: fail_else_unbraced.carbon:[[@LINE+1]]:5: Expected braced code block.
     if (b)
-      // CHECK:STDERR: toolchain/parser/testdata/if/fail_else_unbraced.carbon:[[@LINE+1]]:7: Expected braced code block.
+      // CHECK:STDERR: fail_else_unbraced.carbon:[[@LINE+1]]:7: Expected braced code block.
       c;
     else
-      // CHECK:STDERR: toolchain/parser/testdata/if/fail_else_unbraced.carbon:[[@LINE+1]]:7: Expected braced code block.
+      // CHECK:STDERR: fail_else_unbraced.carbon:[[@LINE+1]]:7: Expected braced code block.
       d;
   else
-    // CHECK:STDERR: toolchain/parser/testdata/if/fail_else_unbraced.carbon:[[@LINE+1]]:5: Expected braced code block.
+    // CHECK:STDERR: fail_else_unbraced.carbon:[[@LINE+1]]:5: Expected braced code block.
     e;
   if (x) { f; }
   else if (x) { g; }
diff --git a/toolchain/parser/testdata/if/fail_errors.carbon b/toolchain/parser/testdata/if/fail_errors.carbon
index 189d31db01a0..c3ac18a457b1 100644
--- a/toolchain/parser/testdata/if/fail_errors.carbon
+++ b/toolchain/parser/testdata/if/fail_errors.carbon
@@ -39,13 +39,13 @@
 // CHECK:STDOUT: ]
 
 fn F() {
-  // CHECK:STDERR: toolchain/parser/testdata/if/fail_errors.carbon:[[@LINE+1]]:6: Expected `(` after `if`.
+  // CHECK:STDERR: fail_errors.carbon:[[@LINE+1]]:6: Expected `(` after `if`.
   if a {}
-  // CHECK:STDERR: toolchain/parser/testdata/if/fail_errors.carbon:[[@LINE+1]]:7: Expected expression.
+  // CHECK:STDERR: fail_errors.carbon:[[@LINE+1]]:7: Expected expression.
   if () {}
-  // CHECK:STDERR: toolchain/parser/testdata/if/fail_errors.carbon:[[@LINE+1]]:9: Unexpected tokens before `)`.
+  // CHECK:STDERR: fail_errors.carbon:[[@LINE+1]]:9: Unexpected tokens before `)`.
   if (b c) {}
   if (d)
-// CHECK:STDERR: toolchain/parser/testdata/if/fail_errors.carbon:[[@LINE+2]]:1: Expected braced code block.
-// CHECK:STDERR: toolchain/parser/testdata/if/fail_errors.carbon:[[@LINE+1]]:1: Expected expression.
+// CHECK:STDERR: fail_errors.carbon:[[@LINE+2]]:1: Expected braced code block.
+// CHECK:STDERR: fail_errors.carbon:[[@LINE+1]]:1: Expected expression.
 }
diff --git a/toolchain/parser/testdata/if/fail_unbraced.carbon b/toolchain/parser/testdata/if/fail_unbraced.carbon
index d3c8ffc0d7d7..7c403e41a14e 100644
--- a/toolchain/parser/testdata/if/fail_unbraced.carbon
+++ b/toolchain/parser/testdata/if/fail_unbraced.carbon
@@ -36,10 +36,10 @@
 
 fn F() {
   if (a)
-    // CHECK:STDERR: toolchain/parser/testdata/if/fail_unbraced.carbon:[[@LINE+1]]:5: Expected braced code block.
+    // CHECK:STDERR: fail_unbraced.carbon:[[@LINE+1]]:5: Expected braced code block.
     if (b)
-      // CHECK:STDERR: toolchain/parser/testdata/if/fail_unbraced.carbon:[[@LINE+1]]:7: Expected braced code block.
+      // CHECK:STDERR: fail_unbraced.carbon:[[@LINE+1]]:7: Expected braced code block.
       if (c)
-        // CHECK:STDERR: toolchain/parser/testdata/if/fail_unbraced.carbon:[[@LINE+1]]:9: Expected braced code block.
+        // CHECK:STDERR: fail_unbraced.carbon:[[@LINE+1]]:9: Expected braced code block.
         d;
 }
diff --git a/toolchain/parser/testdata/operators/fail_infix_uneven_space_after.carbon b/toolchain/parser/testdata/operators/fail_infix_uneven_space_after.carbon
index 09ef8b4a89c2..54d69fc076b8 100644
--- a/toolchain/parser/testdata/operators/fail_infix_uneven_space_after.carbon
+++ b/toolchain/parser/testdata/operators/fail_infix_uneven_space_after.carbon
@@ -17,5 +17,5 @@
 
 // TODO: We could figure out that this first Failed example is infix
 // with one-token lookahead.
-// CHECK:STDERR: toolchain/parser/testdata/operators/fail_infix_uneven_space_after.carbon:[[@LINE+1]]:16: Expected `;` after expression.
+// CHECK:STDERR: fail_infix_uneven_space_after.carbon:[[@LINE+1]]:16: Expected `;` after expression.
 var n: i8 = n* n;
diff --git a/toolchain/parser/testdata/operators/fail_invalid_infix.carbon b/toolchain/parser/testdata/operators/fail_invalid_infix.carbon
index 5f9fbdacdcc0..20605ea9e357 100644
--- a/toolchain/parser/testdata/operators/fail_invalid_infix.carbon
+++ b/toolchain/parser/testdata/operators/fail_invalid_infix.carbon
@@ -34,10 +34,10 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/fail_invalid_infix.carbon:[[@LINE+1]]:19: Expected expression.
+// CHECK:STDERR: fail_invalid_infix.carbon:[[@LINE+1]]:19: Expected expression.
 var a: i32 = n == ;
-// CHECK:STDERR: toolchain/parser/testdata/operators/fail_invalid_infix.carbon:[[@LINE+1]]:14: Expected expression.
+// CHECK:STDERR: fail_invalid_infix.carbon:[[@LINE+1]]:14: Expected expression.
 var b: i32 = == n;
-// CHECK:STDERR: toolchain/parser/testdata/operators/fail_invalid_infix.carbon:[[@LINE+2]]:14: Expected expression.
-// CHECK:STDERR: toolchain/parser/testdata/operators/fail_invalid_infix.carbon:[[@LINE+1]]:17: Expected expression.
+// CHECK:STDERR: fail_invalid_infix.carbon:[[@LINE+2]]:14: Expected expression.
+// CHECK:STDERR: fail_invalid_infix.carbon:[[@LINE+1]]:17: Expected expression.
 var c: i32 = == ;
diff --git a/toolchain/parser/testdata/operators/fail_precedence_and_or.carbon b/toolchain/parser/testdata/operators/fail_precedence_and_or.carbon
index cebeb7aa57d7..6f9ad22e8a2d 100644
--- a/toolchain/parser/testdata/operators/fail_precedence_and_or.carbon
+++ b/toolchain/parser/testdata/operators/fail_precedence_and_or.carbon
@@ -20,6 +20,6 @@
 // CHECK:STDOUT: ]
 
 fn F() {
-  // CHECK:STDERR: toolchain/parser/testdata/operators/fail_precedence_and_or.carbon:[[@LINE+1]]:11: Parentheses are required to disambiguate operator precedence.
+  // CHECK:STDERR: fail_precedence_and_or.carbon:[[@LINE+1]]:11: Parentheses are required to disambiguate operator precedence.
   a and b or c;
 }
diff --git a/toolchain/parser/testdata/operators/fail_precedence_or_and.carbon b/toolchain/parser/testdata/operators/fail_precedence_or_and.carbon
index 02b9fba4325d..e1bcbba27b25 100644
--- a/toolchain/parser/testdata/operators/fail_precedence_or_and.carbon
+++ b/toolchain/parser/testdata/operators/fail_precedence_or_and.carbon
@@ -20,6 +20,6 @@
 // CHECK:STDOUT: ]
 
 fn F() {
-  // CHECK:STDERR: toolchain/parser/testdata/operators/fail_precedence_or_and.carbon:[[@LINE+1]]:10: Parentheses are required to disambiguate operator precedence.
+  // CHECK:STDERR: fail_precedence_or_and.carbon:[[@LINE+1]]:10: Parentheses are required to disambiguate operator precedence.
   a or b and c;
 }
diff --git a/toolchain/parser/testdata/operators/fail_precedence_star_minus.carbon b/toolchain/parser/testdata/operators/fail_precedence_star_minus.carbon
index 01f983a60b1c..e98a79060629 100644
--- a/toolchain/parser/testdata/operators/fail_precedence_star_minus.carbon
+++ b/toolchain/parser/testdata/operators/fail_precedence_star_minus.carbon
@@ -17,5 +17,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/fail_precedence_star_minus.carbon:[[@LINE+1]]:16: Parentheses are required to disambiguate operator precedence.
+// CHECK:STDERR: fail_precedence_star_minus.carbon:[[@LINE+1]]:16: Parentheses are required to disambiguate operator precedence.
 var n: i8 = n* -n;
diff --git a/toolchain/parser/testdata/operators/fail_precedence_star_star.carbon b/toolchain/parser/testdata/operators/fail_precedence_star_star.carbon
index 5f9fdf9ef043..ccbd9cc56c80 100644
--- a/toolchain/parser/testdata/operators/fail_precedence_star_star.carbon
+++ b/toolchain/parser/testdata/operators/fail_precedence_star_star.carbon
@@ -17,5 +17,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/fail_precedence_star_star.carbon:[[@LINE+1]]:16: Parentheses are required to disambiguate operator precedence.
+// CHECK:STDERR: fail_precedence_star_star.carbon:[[@LINE+1]]:16: Parentheses are required to disambiguate operator precedence.
 var n: i8 = n* *p;
diff --git a/toolchain/parser/testdata/operators/fail_star_star_no_space.carbon b/toolchain/parser/testdata/operators/fail_star_star_no_space.carbon
index b3b86eec072d..727e5e6a25ac 100644
--- a/toolchain/parser/testdata/operators/fail_star_star_no_space.carbon
+++ b/toolchain/parser/testdata/operators/fail_star_star_no_space.carbon
@@ -20,5 +20,5 @@
 // before we notice the missing whitespace around the second `*`.
 // It'd be better to (somehow) form n*(*p) and reject due to the missing
 // whitespace around the first `*`.
-// CHECK:STDERR: toolchain/parser/testdata/operators/fail_star_star_no_space.carbon:[[@LINE+1]]:16: Expected `;` after expression.
+// CHECK:STDERR: fail_star_star_no_space.carbon:[[@LINE+1]]:16: Expected `;` after expression.
 var n: i8 = n**p;
diff --git a/toolchain/parser/testdata/operators/fail_variety.carbon b/toolchain/parser/testdata/operators/fail_variety.carbon
index 82d8ac55876a..7d931b742093 100644
--- a/toolchain/parser/testdata/operators/fail_variety.carbon
+++ b/toolchain/parser/testdata/operators/fail_variety.carbon
@@ -35,9 +35,9 @@
 // CHECK:STDOUT: ]
 
 fn F() {
-  // CHECK:STDERR: toolchain/parser/testdata/operators/fail_variety.carbon:[[@LINE+4]]:29: Parentheses are required to disambiguate operator precedence.
-  // CHECK:STDERR: toolchain/parser/testdata/operators/fail_variety.carbon:[[@LINE+3]]:34: Parentheses are required to disambiguate operator precedence.
-  // CHECK:STDERR: toolchain/parser/testdata/operators/fail_variety.carbon:[[@LINE+2]]:38: Parentheses are required to disambiguate operator precedence.
-  // CHECK:STDERR: toolchain/parser/testdata/operators/fail_variety.carbon:[[@LINE+1]]:40: Parentheses are required to disambiguate operator precedence.
+  // CHECK:STDERR: fail_variety.carbon:[[@LINE+4]]:29: Parentheses are required to disambiguate operator precedence.
+  // CHECK:STDERR: fail_variety.carbon:[[@LINE+3]]:34: Parentheses are required to disambiguate operator precedence.
+  // CHECK:STDERR: fail_variety.carbon:[[@LINE+2]]:38: Parentheses are required to disambiguate operator precedence.
+  // CHECK:STDERR: fail_variety.carbon:[[@LINE+1]]:40: Parentheses are required to disambiguate operator precedence.
   n = a * b + c * d = d * d << e & f - not g;
 }
diff --git a/toolchain/parser/testdata/operators/missing_precedence_not.carbon b/toolchain/parser/testdata/operators/missing_precedence_not.carbon
index 419d3dd922e8..f6746107fec8 100644
--- a/toolchain/parser/testdata/operators/missing_precedence_not.carbon
+++ b/toolchain/parser/testdata/operators/missing_precedence_not.carbon
@@ -23,8 +23,8 @@
 // CHECK:STDOUT: ]
 
 fn F() {
-  // CHECK:STDERR: toolchain/parser/testdata/operators/missing_precedence_not.carbon:[[@LINE+3]]:3: Whitespace is required before this unary operator.
-  // CHECK:STDERR: toolchain/parser/testdata/operators/missing_precedence_not.carbon:[[@LINE+2]]:13: Whitespace is required before this unary operator.
-  // CHECK:STDERR: toolchain/parser/testdata/operators/missing_precedence_not.carbon:[[@LINE+1]]:23: Whitespace is required before this unary operator.
+  // CHECK:STDERR: missing_precedence_not.carbon:[[@LINE+3]]:3: Whitespace is required before this unary operator.
+  // CHECK:STDERR: missing_precedence_not.carbon:[[@LINE+2]]:13: Whitespace is required before this unary operator.
+  // CHECK:STDERR: missing_precedence_not.carbon:[[@LINE+1]]:23: Whitespace is required before this unary operator.
   not a and not b and not c;
 }
diff --git a/toolchain/parser/testdata/operators/recover_infix_uneven_space_before.carbon b/toolchain/parser/testdata/operators/recover_infix_uneven_space_before.carbon
index 32847992b3e4..17a53b924e2e 100644
--- a/toolchain/parser/testdata/operators/recover_infix_uneven_space_before.carbon
+++ b/toolchain/parser/testdata/operators/recover_infix_uneven_space_before.carbon
@@ -16,5 +16,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/recover_infix_uneven_space_before.carbon:[[@LINE+1]]:15: Whitespace missing after binary operator.
+// CHECK:STDERR: recover_infix_uneven_space_before.carbon:[[@LINE+1]]:15: Whitespace missing after binary operator.
 var n: i8 = n *n;
diff --git a/toolchain/parser/testdata/operators/recover_postfix_space.carbon b/toolchain/parser/testdata/operators/recover_postfix_space.carbon
index 912847979807..f0d99af17a72 100644
--- a/toolchain/parser/testdata/operators/recover_postfix_space.carbon
+++ b/toolchain/parser/testdata/operators/recover_postfix_space.carbon
@@ -15,5 +15,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/recover_postfix_space.carbon:[[@LINE+1]]:18: Whitespace is not allowed before this unary operator.
+// CHECK:STDERR: recover_postfix_space.carbon:[[@LINE+1]]:18: Whitespace is not allowed before this unary operator.
 var v: type = i8 *;
diff --git a/toolchain/parser/testdata/operators/recover_postfix_space_before_comma.carbon b/toolchain/parser/testdata/operators/recover_postfix_space_before_comma.carbon
index 05c38942875d..3a0a1f1c6192 100644
--- a/toolchain/parser/testdata/operators/recover_postfix_space_before_comma.carbon
+++ b/toolchain/parser/testdata/operators/recover_postfix_space_before_comma.carbon
@@ -20,5 +20,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/recover_postfix_space_before_comma.carbon:[[@LINE+1]]:18: Whitespace is not allowed before this unary operator.
+// CHECK:STDERR: recover_postfix_space_before_comma.carbon:[[@LINE+1]]:18: Whitespace is not allowed before this unary operator.
 var n: i8 = F(i8 *, 0);
diff --git a/toolchain/parser/testdata/operators/recover_postfix_space_in_call.carbon b/toolchain/parser/testdata/operators/recover_postfix_space_in_call.carbon
index 1f32efe32501..ee776c252aa3 100644
--- a/toolchain/parser/testdata/operators/recover_postfix_space_in_call.carbon
+++ b/toolchain/parser/testdata/operators/recover_postfix_space_in_call.carbon
@@ -18,5 +18,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/recover_postfix_space_in_call.carbon:[[@LINE+1]]:18: Whitespace is not allowed before this unary operator.
+// CHECK:STDERR: recover_postfix_space_in_call.carbon:[[@LINE+1]]:18: Whitespace is not allowed before this unary operator.
 var n: i8 = F(i8 *);
diff --git a/toolchain/parser/testdata/operators/recover_postfix_space_surrounding.carbon b/toolchain/parser/testdata/operators/recover_postfix_space_surrounding.carbon
index 76edbb6ef484..0e77453ab909 100644
--- a/toolchain/parser/testdata/operators/recover_postfix_space_surrounding.carbon
+++ b/toolchain/parser/testdata/operators/recover_postfix_space_surrounding.carbon
@@ -15,6 +15,6 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/recover_postfix_space_surrounding.carbon:[[@LINE+2]]:18: Whitespace is not allowed before this unary operator.
-// CHECK:STDERR: toolchain/parser/testdata/operators/recover_postfix_space_surrounding.carbon:[[@LINE+1]]:18: Whitespace is required after this unary operator.
+// CHECK:STDERR: recover_postfix_space_surrounding.carbon:[[@LINE+2]]:18: Whitespace is not allowed before this unary operator.
+// CHECK:STDERR: recover_postfix_space_surrounding.carbon:[[@LINE+1]]:18: Whitespace is required after this unary operator.
 var v: type = i8 * ;
diff --git a/toolchain/parser/testdata/operators/recover_prefix_space.carbon b/toolchain/parser/testdata/operators/recover_prefix_space.carbon
index fa5aac534fae..350e71c8d302 100644
--- a/toolchain/parser/testdata/operators/recover_prefix_space.carbon
+++ b/toolchain/parser/testdata/operators/recover_prefix_space.carbon
@@ -15,6 +15,6 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/recover_prefix_space.carbon:[[@LINE+2]]:13: Whitespace is not allowed after this unary operator.
-// CHECK:STDERR: toolchain/parser/testdata/operators/recover_prefix_space.carbon:[[@LINE+1]]:13: Whitespace is required before this unary operator.
+// CHECK:STDERR: recover_prefix_space.carbon:[[@LINE+2]]:13: Whitespace is not allowed after this unary operator.
+// CHECK:STDERR: recover_prefix_space.carbon:[[@LINE+1]]:13: Whitespace is required before this unary operator.
 var n: i8 = - n;
diff --git a/toolchain/parser/testdata/operators/recover_prefix_uneven_space_with_assign.carbon b/toolchain/parser/testdata/operators/recover_prefix_uneven_space_with_assign.carbon
index 6aa2d8a850cc..80dc9780df75 100644
--- a/toolchain/parser/testdata/operators/recover_prefix_uneven_space_with_assign.carbon
+++ b/toolchain/parser/testdata/operators/recover_prefix_uneven_space_with_assign.carbon
@@ -15,5 +15,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/operators/recover_prefix_uneven_space_with_assign.carbon:[[@LINE+1]]:12: Whitespace is not allowed after this unary operator.
+// CHECK:STDERR: recover_prefix_uneven_space_with_assign.carbon:[[@LINE+1]]:12: Whitespace is not allowed after this unary operator.
 var n: i8 =- n;
diff --git a/toolchain/parser/testdata/package/fail_extra_string.carbon b/toolchain/parser/testdata/package/fail_extra_string.carbon
index 113851d12dc8..aa821d7a3fcd 100644
--- a/toolchain/parser/testdata/package/fail_extra_string.carbon
+++ b/toolchain/parser/testdata/package/fail_extra_string.carbon
@@ -12,5 +12,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/package/fail_extra_string.carbon:[[@LINE+1]]:27: Expected a `api` or `impl`.
+// CHECK:STDERR: fail_extra_string.carbon:[[@LINE+1]]:27: Expected a `api` or `impl`.
 package Foo library "bar" "baz";
diff --git a/toolchain/parser/testdata/package/fail_library_is_identifier.carbon b/toolchain/parser/testdata/package/fail_library_is_identifier.carbon
index 3b2bbd59043b..af81402e82e4 100644
--- a/toolchain/parser/testdata/package/fail_library_is_identifier.carbon
+++ b/toolchain/parser/testdata/package/fail_library_is_identifier.carbon
@@ -10,5 +10,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/package/fail_library_is_identifier.carbon:[[@LINE+1]]:26: Expected a string literal to specify the library name.
+// CHECK:STDERR: fail_library_is_identifier.carbon:[[@LINE+1]]:26: Expected a string literal to specify the library name.
 package Geometry library Shapes api;
diff --git a/toolchain/parser/testdata/package/fail_library_skips_name.carbon b/toolchain/parser/testdata/package/fail_library_skips_name.carbon
index e1febd2167e3..acf1bf82777c 100644
--- a/toolchain/parser/testdata/package/fail_library_skips_name.carbon
+++ b/toolchain/parser/testdata/package/fail_library_skips_name.carbon
@@ -9,5 +9,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/package/fail_library_skips_name.carbon:[[@LINE+1]]:9: Expected identifier after `package`.
+// CHECK:STDERR: fail_library_skips_name.carbon:[[@LINE+1]]:9: Expected identifier after `package`.
 package library "Shapes" api;
diff --git a/toolchain/parser/testdata/package/fail_name_is_keyword.carbon b/toolchain/parser/testdata/package/fail_name_is_keyword.carbon
index 459a58b88952..aef11828990b 100644
--- a/toolchain/parser/testdata/package/fail_name_is_keyword.carbon
+++ b/toolchain/parser/testdata/package/fail_name_is_keyword.carbon
@@ -9,5 +9,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/package/fail_name_is_keyword.carbon:[[@LINE+1]]:9: Expected identifier after `package`.
+// CHECK:STDERR: fail_name_is_keyword.carbon:[[@LINE+1]]:9: Expected identifier after `package`.
 package fn;
diff --git a/toolchain/parser/testdata/package/fail_no_name.carbon b/toolchain/parser/testdata/package/fail_no_name.carbon
index 5125aeb8abe9..4a29360ff8b3 100644
--- a/toolchain/parser/testdata/package/fail_no_name.carbon
+++ b/toolchain/parser/testdata/package/fail_no_name.carbon
@@ -9,5 +9,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/package/fail_no_name.carbon:[[@LINE+1]]:8: Expected identifier after `package`.
+// CHECK:STDERR: fail_no_name.carbon:[[@LINE+1]]:8: Expected identifier after `package`.
 package;
diff --git a/toolchain/parser/testdata/package/fail_no_semi.carbon b/toolchain/parser/testdata/package/fail_no_semi.carbon
index d85b4313cff6..e6b57461ea65 100644
--- a/toolchain/parser/testdata/package/fail_no_semi.carbon
+++ b/toolchain/parser/testdata/package/fail_no_semi.carbon
@@ -11,5 +11,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/package/fail_no_semi.carbon:[[@LINE+1]]:21: Expected `;` to end package directive.
+// CHECK:STDERR: fail_no_semi.carbon:[[@LINE+1]]:21: Expected `;` to end package directive.
 package Geometry api
diff --git a/toolchain/parser/testdata/package/fail_no_type.carbon b/toolchain/parser/testdata/package/fail_no_type.carbon
index 2f16954118f7..767235a35d22 100644
--- a/toolchain/parser/testdata/package/fail_no_type.carbon
+++ b/toolchain/parser/testdata/package/fail_no_type.carbon
@@ -10,5 +10,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/package/fail_no_type.carbon:[[@LINE+1]]:17: Expected a `api` or `impl`.
+// CHECK:STDERR: fail_no_type.carbon:[[@LINE+1]]:17: Expected a `api` or `impl`.
 package Geometry;
diff --git a/toolchain/parser/testdata/package/fail_omit_library_keyword.carbon b/toolchain/parser/testdata/package/fail_omit_library_keyword.carbon
index cd8d94b992e4..02413356a6d8 100644
--- a/toolchain/parser/testdata/package/fail_omit_library_keyword.carbon
+++ b/toolchain/parser/testdata/package/fail_omit_library_keyword.carbon
@@ -10,5 +10,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/package/fail_omit_library_keyword.carbon:[[@LINE+1]]:18: Missing `library` keyword.
+// CHECK:STDERR: fail_omit_library_keyword.carbon:[[@LINE+1]]:18: Missing `library` keyword.
 package Geometry "Shapes" api;
diff --git a/toolchain/parser/testdata/return/fail_expr_no_semi.carbon b/toolchain/parser/testdata/return/fail_expr_no_semi.carbon
index 3d42eeed71f4..ca2c4c32b521 100644
--- a/toolchain/parser/testdata/return/fail_expr_no_semi.carbon
+++ b/toolchain/parser/testdata/return/fail_expr_no_semi.carbon
@@ -18,5 +18,5 @@
 
 fn F() {
   return x
-// CHECK:STDERR: toolchain/parser/testdata/return/fail_expr_no_semi.carbon:[[@LINE+1]]:1: Expected `;` after `return`.
+// CHECK:STDERR: fail_expr_no_semi.carbon:[[@LINE+1]]:1: Expected `;` after `return`.
 }
diff --git a/toolchain/parser/testdata/return/fail_no_semi.carbon b/toolchain/parser/testdata/return/fail_no_semi.carbon
index 54457d0e7e3d..6307617f278f 100644
--- a/toolchain/parser/testdata/return/fail_no_semi.carbon
+++ b/toolchain/parser/testdata/return/fail_no_semi.carbon
@@ -18,6 +18,6 @@
 
 fn F() {
   return
-// CHECK:STDERR: toolchain/parser/testdata/return/fail_no_semi.carbon:[[@LINE+2]]:1: Expected expression.
-// CHECK:STDERR: toolchain/parser/testdata/return/fail_no_semi.carbon:[[@LINE+1]]:1: Expected `;` after `return`.
+// CHECK:STDERR: fail_no_semi.carbon:[[@LINE+2]]:1: Expected expression.
+// CHECK:STDERR: fail_no_semi.carbon:[[@LINE+1]]:1: Expected `;` after `return`.
 }
diff --git a/toolchain/parser/testdata/struct/fail_comma_only.carbon b/toolchain/parser/testdata/struct/fail_comma_only.carbon
index 006e12e9f242..4c31b6115fa9 100644
--- a/toolchain/parser/testdata/struct/fail_comma_only.carbon
+++ b/toolchain/parser/testdata/struct/fail_comma_only.carbon
@@ -18,5 +18,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_comma_only.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
+// CHECK:STDERR: fail_comma_only.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
 var x: {,} = {};
diff --git a/toolchain/parser/testdata/struct/fail_comma_repeat_in_type.carbon b/toolchain/parser/testdata/struct/fail_comma_repeat_in_type.carbon
index d8f1dd70f97b..9056c70a316e 100644
--- a/toolchain/parser/testdata/struct/fail_comma_repeat_in_type.carbon
+++ b/toolchain/parser/testdata/struct/fail_comma_repeat_in_type.carbon
@@ -23,5 +23,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_comma_repeat_in_type.carbon:[[@LINE+1]]:17: Expected `.field: field_type`.
+// CHECK:STDERR: fail_comma_repeat_in_type.carbon:[[@LINE+1]]:17: Expected `.field: field_type`.
 var x: {.a: i32,,} = {};
diff --git a/toolchain/parser/testdata/struct/fail_comma_repeat_in_value.carbon b/toolchain/parser/testdata/struct/fail_comma_repeat_in_value.carbon
index cbce89274aad..5998eaf228ae 100644
--- a/toolchain/parser/testdata/struct/fail_comma_repeat_in_value.carbon
+++ b/toolchain/parser/testdata/struct/fail_comma_repeat_in_value.carbon
@@ -23,5 +23,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_comma_repeat_in_value.carbon:[[@LINE+1]]:16: Expected `.field = value`.
+// CHECK:STDERR: fail_comma_repeat_in_value.carbon:[[@LINE+1]]:16: Expected `.field = value`.
 var x: {.a = 0,,} = {};
diff --git a/toolchain/parser/testdata/struct/fail_dot_only.carbon b/toolchain/parser/testdata/struct/fail_dot_only.carbon
index 97cef75d6777..6ec238f2c22b 100644
--- a/toolchain/parser/testdata/struct/fail_dot_only.carbon
+++ b/toolchain/parser/testdata/struct/fail_dot_only.carbon
@@ -19,5 +19,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_dot_only.carbon:[[@LINE+1]]:10: Expected identifier after `.`.
+// CHECK:STDERR: fail_dot_only.carbon:[[@LINE+1]]:10: Expected identifier after `.`.
 var x: {.} = {};
diff --git a/toolchain/parser/testdata/struct/fail_dot_string_colon.carbon b/toolchain/parser/testdata/struct/fail_dot_string_colon.carbon
index 092b27d461df..e607f8f677a7 100644
--- a/toolchain/parser/testdata/struct/fail_dot_string_colon.carbon
+++ b/toolchain/parser/testdata/struct/fail_dot_string_colon.carbon
@@ -25,5 +25,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_dot_string_colon.carbon:[[@LINE+1]]:10: Expected identifier after `.`.
+// CHECK:STDERR: fail_dot_string_colon.carbon:[[@LINE+1]]:10: Expected identifier after `.`.
 var x: {."hello": i32, .y: i32} = {};
diff --git a/toolchain/parser/testdata/struct/fail_dot_string_equals.carbon b/toolchain/parser/testdata/struct/fail_dot_string_equals.carbon
index 3bd4e84b11cb..f93e3ff47dc4 100644
--- a/toolchain/parser/testdata/struct/fail_dot_string_equals.carbon
+++ b/toolchain/parser/testdata/struct/fail_dot_string_equals.carbon
@@ -25,5 +25,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_dot_string_equals.carbon:[[@LINE+1]]:10: Expected identifier after `.`.
+// CHECK:STDERR: fail_dot_string_equals.carbon:[[@LINE+1]]:10: Expected identifier after `.`.
 var x: {."hello" = 0, .y = 4} = {};
diff --git a/toolchain/parser/testdata/struct/fail_extra_token_in_type.carbon b/toolchain/parser/testdata/struct/fail_extra_token_in_type.carbon
index 8ff218db9827..4c2d40e4a4cd 100644
--- a/toolchain/parser/testdata/struct/fail_extra_token_in_type.carbon
+++ b/toolchain/parser/testdata/struct/fail_extra_token_in_type.carbon
@@ -24,5 +24,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_extra_token_in_type.carbon:[[@LINE+1]]:17: Expected `,` or `}`.
+// CHECK:STDERR: fail_extra_token_in_type.carbon:[[@LINE+1]]:17: Expected `,` or `}`.
 var x: {.a: i32 banana} = {.a = 0};
diff --git a/toolchain/parser/testdata/struct/fail_extra_token_in_value.carbon b/toolchain/parser/testdata/struct/fail_extra_token_in_value.carbon
index a450d48309e2..49a7eeef77a4 100644
--- a/toolchain/parser/testdata/struct/fail_extra_token_in_value.carbon
+++ b/toolchain/parser/testdata/struct/fail_extra_token_in_value.carbon
@@ -24,5 +24,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_extra_token_in_value.carbon:[[@LINE+1]]:28: Expected `,` or `}`.
+// CHECK:STDERR: fail_extra_token_in_value.carbon:[[@LINE+1]]:28: Expected `,` or `}`.
 var x: {.a: i32} = {.a = 0 banana};
diff --git a/toolchain/parser/testdata/struct/fail_identifier_colon.carbon b/toolchain/parser/testdata/struct/fail_identifier_colon.carbon
index ba9ae32b292a..3288ce13780c 100644
--- a/toolchain/parser/testdata/struct/fail_identifier_colon.carbon
+++ b/toolchain/parser/testdata/struct/fail_identifier_colon.carbon
@@ -17,5 +17,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_identifier_colon.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
+// CHECK:STDERR: fail_identifier_colon.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
 var x: {a:} = {};
diff --git a/toolchain/parser/testdata/struct/fail_identifier_equals.carbon b/toolchain/parser/testdata/struct/fail_identifier_equals.carbon
index aa7aa30b1ca7..53d3b9b1728e 100644
--- a/toolchain/parser/testdata/struct/fail_identifier_equals.carbon
+++ b/toolchain/parser/testdata/struct/fail_identifier_equals.carbon
@@ -17,5 +17,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_identifier_equals.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
+// CHECK:STDERR: fail_identifier_equals.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
 var x: {a=} = {};
diff --git a/toolchain/parser/testdata/struct/fail_identifier_only.carbon b/toolchain/parser/testdata/struct/fail_identifier_only.carbon
index 4e08bc83d8ff..2d30f444d65d 100644
--- a/toolchain/parser/testdata/struct/fail_identifier_only.carbon
+++ b/toolchain/parser/testdata/struct/fail_identifier_only.carbon
@@ -17,5 +17,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_identifier_only.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
+// CHECK:STDERR: fail_identifier_only.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
 var x: {a} = {};
diff --git a/toolchain/parser/testdata/struct/fail_missing_type.carbon b/toolchain/parser/testdata/struct/fail_missing_type.carbon
index 8273e0934553..0824bb95a810 100644
--- a/toolchain/parser/testdata/struct/fail_missing_type.carbon
+++ b/toolchain/parser/testdata/struct/fail_missing_type.carbon
@@ -20,5 +20,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_missing_type.carbon:[[@LINE+1]]:12: Expected expression.
+// CHECK:STDERR: fail_missing_type.carbon:[[@LINE+1]]:12: Expected expression.
 var x: {.a:} = {};
diff --git a/toolchain/parser/testdata/struct/fail_missing_value.carbon b/toolchain/parser/testdata/struct/fail_missing_value.carbon
index f2856bf7f90b..26d22c943854 100644
--- a/toolchain/parser/testdata/struct/fail_missing_value.carbon
+++ b/toolchain/parser/testdata/struct/fail_missing_value.carbon
@@ -20,5 +20,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_missing_value.carbon:[[@LINE+1]]:12: Expected expression.
+// CHECK:STDERR: fail_missing_value.carbon:[[@LINE+1]]:12: Expected expression.
 var x: {.a=} = {};
diff --git a/toolchain/parser/testdata/struct/fail_mix_type_and_value.carbon b/toolchain/parser/testdata/struct/fail_mix_type_and_value.carbon
index d67915f417cb..4f1e05dd07b6 100644
--- a/toolchain/parser/testdata/struct/fail_mix_type_and_value.carbon
+++ b/toolchain/parser/testdata/struct/fail_mix_type_and_value.carbon
@@ -24,5 +24,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_mix_type_and_value.carbon:[[@LINE+1]]:21: Expected `.field: field_type`.
+// CHECK:STDERR: fail_mix_type_and_value.carbon:[[@LINE+1]]:21: Expected `.field: field_type`.
 var x: {.a: i32, .b = 0} = {};
diff --git a/toolchain/parser/testdata/struct/fail_mix_value_and_type.carbon b/toolchain/parser/testdata/struct/fail_mix_value_and_type.carbon
index 8ba22a09bd76..365b296e8da8 100644
--- a/toolchain/parser/testdata/struct/fail_mix_value_and_type.carbon
+++ b/toolchain/parser/testdata/struct/fail_mix_value_and_type.carbon
@@ -22,5 +22,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_mix_value_and_type.carbon:[[@LINE+1]]:17: Expected `.field = value`.
+// CHECK:STDERR: fail_mix_value_and_type.carbon:[[@LINE+1]]:17: Expected `.field = value`.
 var x: {.a = 0, b: i32} = {};
diff --git a/toolchain/parser/testdata/struct/fail_mix_with_unknown.carbon b/toolchain/parser/testdata/struct/fail_mix_with_unknown.carbon
index 2383e2075943..85993938feda 100644
--- a/toolchain/parser/testdata/struct/fail_mix_with_unknown.carbon
+++ b/toolchain/parser/testdata/struct/fail_mix_with_unknown.carbon
@@ -47,10 +47,10 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_mix_with_unknown.carbon:[[@LINE+2]]:25: Expected `.field = value`.
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_mix_with_unknown.carbon:[[@LINE+1]]:29: Expected `.field = value`.
+// CHECK:STDERR: fail_mix_with_unknown.carbon:[[@LINE+2]]:25: Expected `.field = value`.
+// CHECK:STDERR: fail_mix_with_unknown.carbon:[[@LINE+1]]:29: Expected `.field = value`.
 var x: i32 = {.a = 1, .b, .c: i32};
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_mix_with_unknown.carbon:[[@LINE+2]]:26: Expected `.field: field_type`.
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_mix_with_unknown.carbon:[[@LINE+1]]:31: Expected `.field: field_type`.
+// CHECK:STDERR: fail_mix_with_unknown.carbon:[[@LINE+2]]:26: Expected `.field: field_type`.
+// CHECK:STDERR: fail_mix_with_unknown.carbon:[[@LINE+1]]:31: Expected `.field: field_type`.
 var x: i32 = {.a: i32, .b, .c = 1};
diff --git a/toolchain/parser/testdata/struct/fail_no_colon_or_equals.carbon b/toolchain/parser/testdata/struct/fail_no_colon_or_equals.carbon
index 8935dba73067..4442a363d107 100644
--- a/toolchain/parser/testdata/struct/fail_no_colon_or_equals.carbon
+++ b/toolchain/parser/testdata/struct/fail_no_colon_or_equals.carbon
@@ -19,5 +19,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_no_colon_or_equals.carbon:[[@LINE+1]]:11: Expected `.field: field_type` or `.field = value`.
+// CHECK:STDERR: fail_no_colon_or_equals.carbon:[[@LINE+1]]:11: Expected `.field: field_type` or `.field = value`.
 var x: {.a} = {};
diff --git a/toolchain/parser/testdata/struct/fail_type_no_designator.carbon b/toolchain/parser/testdata/struct/fail_type_no_designator.carbon
index ce95a10fea13..28f43e013f8d 100644
--- a/toolchain/parser/testdata/struct/fail_type_no_designator.carbon
+++ b/toolchain/parser/testdata/struct/fail_type_no_designator.carbon
@@ -17,5 +17,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/struct/fail_type_no_designator.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
+// CHECK:STDERR: fail_type_no_designator.carbon:[[@LINE+1]]:9: Expected `.field: field_type` or `.field = value`.
 var x: {i32} = {};
diff --git a/toolchain/parser/testdata/var/fail_bad_name.carbon b/toolchain/parser/testdata/var/fail_bad_name.carbon
index b19112dbc9f4..47ab7b87c40f 100644
--- a/toolchain/parser/testdata/var/fail_bad_name.carbon
+++ b/toolchain/parser/testdata/var/fail_bad_name.carbon
@@ -12,5 +12,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/var/fail_bad_name.carbon:[[@LINE+1]]:5: Expected pattern in `var` declaration.
+// CHECK:STDERR: fail_bad_name.carbon:[[@LINE+1]]:5: Expected pattern in `var` declaration.
 var *;
diff --git a/toolchain/parser/testdata/var/fail_empty.carbon b/toolchain/parser/testdata/var/fail_empty.carbon
index b33018175cba..ea357390fc61 100644
--- a/toolchain/parser/testdata/var/fail_empty.carbon
+++ b/toolchain/parser/testdata/var/fail_empty.carbon
@@ -12,5 +12,5 @@
 // CHECK:STDOUT: {kind: 'FileEnd', text: ''},
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/parser/testdata/var/fail_empty.carbon:[[@LINE+1]]:4: Expected pattern in `var` declaration.
+// CHECK:STDERR: fail_empty.carbon:[[@LINE+1]]:4: Expected pattern in `var` declaration.
 var;
diff --git a/toolchain/parser/testdata/while/fail_no_semi.carbon b/toolchain/parser/testdata/while/fail_no_semi.carbon
index db9c4c4f9f24..1f691b706523 100644
--- a/toolchain/parser/testdata/while/fail_no_semi.carbon
+++ b/toolchain/parser/testdata/while/fail_no_semi.carbon
@@ -39,11 +39,11 @@ fn F() {
   while (a) {
     if (b) {
       break
-    // CHECK:STDERR: toolchain/parser/testdata/while/fail_no_semi.carbon:[[@LINE+1]]:5: Expected `;` after `break`.
+    // CHECK:STDERR: fail_no_semi.carbon:[[@LINE+1]]:5: Expected `;` after `break`.
     }
     if (c) {
       continue
-    // CHECK:STDERR: toolchain/parser/testdata/while/fail_no_semi.carbon:[[@LINE+1]]:5: Expected `;` after `continue`.
+    // CHECK:STDERR: fail_no_semi.carbon:[[@LINE+1]]:5: Expected `;` after `continue`.
     }
   }
 }
diff --git a/toolchain/parser/testdata/while/fail_unbraced.carbon b/toolchain/parser/testdata/while/fail_unbraced.carbon
index 3bf046117212..5048af1197ff 100644
--- a/toolchain/parser/testdata/while/fail_unbraced.carbon
+++ b/toolchain/parser/testdata/while/fail_unbraced.carbon
@@ -24,6 +24,6 @@
 
 fn F() {
   while (a)
-    // CHECK:STDERR: toolchain/parser/testdata/while/fail_unbraced.carbon:[[@LINE+1]]:5: Expected braced code block.
+    // CHECK:STDERR: fail_unbraced.carbon:[[@LINE+1]]:5: Expected braced code block.
     break;
 }
diff --git a/toolchain/semantics/semantics_file_test.cpp b/toolchain/semantics/semantics_file_test.cpp
index fc8ba251ae6e..d00307a3fca5 100644
--- a/toolchain/semantics/semantics_file_test.cpp
+++ b/toolchain/semantics/semantics_file_test.cpp
@@ -17,21 +17,25 @@ namespace {
 
 class SemanticsFileTest : public FileTestBase {
  public:
-  explicit SemanticsFileTest(llvm::StringRef path) : FileTestBase(path) {}
+  explicit SemanticsFileTest(const std::filesystem::path& path)
+      : FileTestBase(path) {}
 
   auto RunOverFile(llvm::raw_ostream& stdout, llvm::raw_ostream& stderr)
       -> bool override {
     Driver driver(stdout, stderr);
-    return driver.RunFullCommand({"dump", "semantics-ir", path()});
+    return driver.RunFullCommand(
+        {"dump", "semantics-ir", path().filename().string()});
   }
 };
 
 }  // namespace
 
-auto RegisterFileTests(const std::vector<llvm::StringRef>& paths) -> void {
-  SemanticsFileTest::RegisterTests(
-      "SemanticsFileTest", paths,
-      [](llvm::StringRef path) { return new SemanticsFileTest(path); });
+auto RegisterFileTests(const std::vector<std::filesystem::path>& paths)
+    -> void {
+  SemanticsFileTest::RegisterTests("SemanticsFileTest", paths,
+                                   [](const std::filesystem::path& path) {
+                                     return new SemanticsFileTest(path);
+                                   });
 }
 
 }  // namespace Carbon::Testing
diff --git a/toolchain/semantics/testdata/basics/fail_name_lookup.carbon b/toolchain/semantics/testdata/basics/fail_name_lookup.carbon
index ba0bee0e4eff..ba823e04aa61 100644
--- a/toolchain/semantics/testdata/basics/fail_name_lookup.carbon
+++ b/toolchain/semantics/testdata/basics/fail_name_lookup.carbon
@@ -30,6 +30,6 @@
 // CHECK:STDOUT: ]
 
 fn Main() {
-  // CHECK:STDERR: toolchain/semantics/testdata/basics/fail_name_lookup.carbon:[[@LINE+1]]:3: Name x not found
+  // CHECK:STDERR: fail_name_lookup.carbon:[[@LINE+1]]:3: Name x not found
   x;
 }
diff --git a/toolchain/semantics/testdata/designators/fail_unsupported.carbon b/toolchain/semantics/testdata/designators/fail_unsupported.carbon
index d7160ec24e85..808fb576b879 100644
--- a/toolchain/semantics/testdata/designators/fail_unsupported.carbon
+++ b/toolchain/semantics/testdata/designators/fail_unsupported.carbon
@@ -37,5 +37,5 @@
 // CHECK:STDOUT: ]
 
 var x: i32;
-// CHECK:STDERR: toolchain/semantics/testdata/designators/fail_unsupported.carbon:[[@LINE+1]]:15: Type `i32` does not support designator expressions.
+// CHECK:STDERR: fail_unsupported.carbon:[[@LINE+1]]:15: Type `i32` does not support designator expressions.
 var y: i32 = x.b;
diff --git a/toolchain/semantics/testdata/function/call/fail_param_count.carbon b/toolchain/semantics/testdata/function/call/fail_param_count.carbon
index 1d3cd6ed9c3f..cf443771b7e6 100644
--- a/toolchain/semantics/testdata/function/call/fail_param_count.carbon
+++ b/toolchain/semantics/testdata/function/call/fail_param_count.carbon
@@ -129,24 +129,24 @@ fn Run1(a: i32) {}
 fn Run2(a: i32, b: i32) {}
 
 fn Main() {
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE-6]]:1: Callable cannot be used: Received 1 argument(s), but require 0 argument(s).
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE-6]]:1: Callable cannot be used: Received 1 argument(s), but require 0 argument(s).
   Run0(1);
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE-9]]:1: Callable cannot be used: Received 2 argument(s), but require 0 argument(s).
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE-9]]:1: Callable cannot be used: Received 2 argument(s), but require 0 argument(s).
   Run0(0, 1);
 
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE-12]]:1: Callable cannot be used: Received 0 argument(s), but require 1 argument(s).
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE-12]]:1: Callable cannot be used: Received 0 argument(s), but require 1 argument(s).
   Run1();
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE-15]]:1: Callable cannot be used: Received 2 argument(s), but require 1 argument(s).
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE-15]]:1: Callable cannot be used: Received 2 argument(s), but require 1 argument(s).
   Run1(0, 1);
 
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE-18]]:1: Callable cannot be used: Received 0 argument(s), but require 2 argument(s).
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE-18]]:1: Callable cannot be used: Received 0 argument(s), but require 2 argument(s).
   Run2();
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_count.carbon:[[@LINE-21]]:1: Callable cannot be used: Received 1 argument(s), but require 2 argument(s).
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE+2]]:7: No matching callable was found.
+  // CHECK:STDERR: fail_param_count.carbon:[[@LINE-21]]:1: Callable cannot be used: Received 1 argument(s), but require 2 argument(s).
   Run2(0);
 }
diff --git a/toolchain/semantics/testdata/function/call/fail_param_type.carbon b/toolchain/semantics/testdata/function/call/fail_param_type.carbon
index 5bd11eb25f20..76e597172c2d 100644
--- a/toolchain/semantics/testdata/function/call/fail_param_type.carbon
+++ b/toolchain/semantics/testdata/function/call/fail_param_type.carbon
@@ -58,7 +58,7 @@
 fn Run(a: i32) {}
 
 fn Main() {
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_type.carbon:[[@LINE+2]]:6: No matching callable was found.
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_param_type.carbon:[[@LINE-4]]:1: Callable cannot be used: Cannot implicityly convert argument 0 from `f64` to `i32`.
+  // CHECK:STDERR: fail_param_type.carbon:[[@LINE+2]]:6: No matching callable was found.
+  // CHECK:STDERR: fail_param_type.carbon:[[@LINE-4]]:1: Callable cannot be used: Cannot implicityly convert argument 0 from `f64` to `i32`.
   Run(1.0);
 }
diff --git a/toolchain/semantics/testdata/function/call/fail_return_type_mismatch.carbon b/toolchain/semantics/testdata/function/call/fail_return_type_mismatch.carbon
index 2b540d2c8026..a683596cc7c2 100644
--- a/toolchain/semantics/testdata/function/call/fail_return_type_mismatch.carbon
+++ b/toolchain/semantics/testdata/function/call/fail_return_type_mismatch.carbon
@@ -57,6 +57,6 @@
 fn Foo() -> f64 { return 1.0; }
 
 fn Run() {
-  // CHECK:STDERR: toolchain/semantics/testdata/function/call/fail_return_type_mismatch.carbon:[[@LINE+1]]:21: Cannot implicitly convert from `f64` to `i32`.
+  // CHECK:STDERR: fail_return_type_mismatch.carbon:[[@LINE+1]]:21: Cannot implicitly convert from `f64` to `i32`.
   var x: i32 = Foo();
 }
diff --git a/toolchain/semantics/testdata/function/definition/fail_param_name_conflict.carbon b/toolchain/semantics/testdata/function/definition/fail_param_name_conflict.carbon
index 5c127c0c85ce..c94f681d6fb8 100644
--- a/toolchain/semantics/testdata/function/definition/fail_param_name_conflict.carbon
+++ b/toolchain/semantics/testdata/function/definition/fail_param_name_conflict.carbon
@@ -44,6 +44,6 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/semantics/testdata/function/definition/fail_param_name_conflict.carbon:[[@LINE+2]]:16: Redefining a in the same scope.
-// CHECK:STDERR: toolchain/semantics/testdata/function/definition/fail_param_name_conflict.carbon:[[@LINE+1]]:8: Previous definition is here.
+// CHECK:STDERR: fail_param_name_conflict.carbon:[[@LINE+2]]:16: Redefining a in the same scope.
+// CHECK:STDERR: fail_param_name_conflict.carbon:[[@LINE+1]]:8: Previous definition is here.
 fn Bar(a: i32, a: i32) {}
diff --git a/toolchain/semantics/testdata/operators/fail_type_mismatch.carbon b/toolchain/semantics/testdata/operators/fail_type_mismatch.carbon
index b375acea7d21..89df468d87ce 100644
--- a/toolchain/semantics/testdata/operators/fail_type_mismatch.carbon
+++ b/toolchain/semantics/testdata/operators/fail_type_mismatch.carbon
@@ -42,6 +42,6 @@
 // CHECK:STDOUT: ]
 
 fn Main() -> i32 {
-  // CHECK:STDERR: toolchain/semantics/testdata/operators/fail_type_mismatch.carbon:[[@LINE+1]]:13: Cannot implicitly convert from `i32` to `f64`.
+  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+1]]:13: Cannot implicitly convert from `i32` to `f64`.
   return 12 + 3.4;
 }
diff --git a/toolchain/semantics/testdata/operators/fail_type_mismatch_once.carbon b/toolchain/semantics/testdata/operators/fail_type_mismatch_once.carbon
index c77b6209dd26..b707614a4f2b 100644
--- a/toolchain/semantics/testdata/operators/fail_type_mismatch_once.carbon
+++ b/toolchain/semantics/testdata/operators/fail_type_mismatch_once.carbon
@@ -49,6 +49,6 @@
 fn Main() -> i32 {
   // The following line has two mismatches, but after the first, it shouldn't
   // keep erroring.
-  // CHECK:STDERR: toolchain/semantics/testdata/operators/fail_type_mismatch_once.carbon:[[@LINE+1]]:13: Cannot implicitly convert from `i32` to `f64`.
+  // CHECK:STDERR: fail_type_mismatch_once.carbon:[[@LINE+1]]:13: Cannot implicitly convert from `i32` to `f64`.
   return 12 + 3.4 + 12;
 }
diff --git a/toolchain/semantics/testdata/return/fail_type_mismatch.carbon b/toolchain/semantics/testdata/return/fail_type_mismatch.carbon
index 65c8e949ab06..d45ab575085b 100644
--- a/toolchain/semantics/testdata/return/fail_type_mismatch.carbon
+++ b/toolchain/semantics/testdata/return/fail_type_mismatch.carbon
@@ -37,6 +37,6 @@
 // CHECK:STDOUT: ]
 
 fn Main() -> i32 {
-  // CHECK:STDERR: toolchain/semantics/testdata/return/fail_type_mismatch.carbon:[[@LINE+1]]:13: Cannot implicitly convert from `f64` to `i32`.
+  // CHECK:STDERR: fail_type_mismatch.carbon:[[@LINE+1]]:13: Cannot implicitly convert from `f64` to `i32`.
   return 1.0;
 }
diff --git a/toolchain/semantics/testdata/return/fail_value_disallowed.carbon b/toolchain/semantics/testdata/return/fail_value_disallowed.carbon
index 8fa4b6157e5a..0a38a55037d5 100644
--- a/toolchain/semantics/testdata/return/fail_value_disallowed.carbon
+++ b/toolchain/semantics/testdata/return/fail_value_disallowed.carbon
@@ -37,7 +37,7 @@
 // CHECK:STDOUT: ]
 
 fn Main() {
-  // CHECK:STDERR: toolchain/semantics/testdata/return/fail_value_disallowed.carbon:[[@LINE+2]]:11: No return expression should be provided in this context.
-  // CHECK:STDERR: toolchain/semantics/testdata/return/fail_value_disallowed.carbon:[[@LINE-2]]:1: There was no return type provided.
+  // CHECK:STDERR: fail_value_disallowed.carbon:[[@LINE+2]]:11: No return expression should be provided in this context.
+  // CHECK:STDERR: fail_value_disallowed.carbon:[[@LINE-2]]:1: There was no return type provided.
   return 0;
 }
diff --git a/toolchain/semantics/testdata/return/fail_value_missing.carbon b/toolchain/semantics/testdata/return/fail_value_missing.carbon
index d3c20ef56275..8b0e8cbb344b 100644
--- a/toolchain/semantics/testdata/return/fail_value_missing.carbon
+++ b/toolchain/semantics/testdata/return/fail_value_missing.carbon
@@ -34,6 +34,6 @@
 // CHECK:STDOUT: ]
 
 fn Main() -> i32 {
-  // CHECK:STDERR: toolchain/semantics/testdata/return/fail_value_missing.carbon:[[@LINE+1]]:9: Must return a i32.
+  // CHECK:STDERR: fail_value_missing.carbon:[[@LINE+1]]:9: Must return a i32.
   return;
 }
diff --git a/toolchain/semantics/testdata/struct/fail_assign_empty.carbon b/toolchain/semantics/testdata/struct/fail_assign_empty.carbon
index d2caf1459875..1e107fb99b68 100644
--- a/toolchain/semantics/testdata/struct/fail_assign_empty.carbon
+++ b/toolchain/semantics/testdata/struct/fail_assign_empty.carbon
@@ -40,5 +40,5 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/semantics/testdata/struct/fail_assign_empty.carbon:[[@LINE+1]]:22: Cannot implicitly convert from `{} as Type` to `{.a: i32}`.
+// CHECK:STDERR: fail_assign_empty.carbon:[[@LINE+1]]:22: Cannot implicitly convert from `{} as Type` to `{.a: i32}`.
 var x: {.a: i32} = {};
diff --git a/toolchain/semantics/testdata/struct/fail_assign_to_empty.carbon b/toolchain/semantics/testdata/struct/fail_assign_to_empty.carbon
index 6a88a2bdbf3a..b7b357046193 100644
--- a/toolchain/semantics/testdata/struct/fail_assign_to_empty.carbon
+++ b/toolchain/semantics/testdata/struct/fail_assign_to_empty.carbon
@@ -49,5 +49,5 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/semantics/testdata/struct/fail_assign_to_empty.carbon:[[@LINE+1]]:21: Cannot implicitly convert from `{.a: i32}` to `{} as Type`.
+// CHECK:STDERR: fail_assign_to_empty.carbon:[[@LINE+1]]:21: Cannot implicitly convert from `{.a: i32}` to `{} as Type`.
 var x: {} = {.a = 1};
diff --git a/toolchain/semantics/testdata/struct/fail_field_name_mismatch.carbon b/toolchain/semantics/testdata/struct/fail_field_name_mismatch.carbon
index a84080b558d3..9eaa7610c592 100644
--- a/toolchain/semantics/testdata/struct/fail_field_name_mismatch.carbon
+++ b/toolchain/semantics/testdata/struct/fail_field_name_mismatch.carbon
@@ -59,5 +59,5 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/semantics/testdata/struct/fail_field_name_mismatch.carbon:[[@LINE+1]]:28: Cannot implicitly convert from `{.b: i32}` to `{.a: i32}`.
+// CHECK:STDERR: fail_field_name_mismatch.carbon:[[@LINE+1]]:28: Cannot implicitly convert from `{.b: i32}` to `{.a: i32}`.
 var x: {.a: i32} = {.b = 1};
diff --git a/toolchain/semantics/testdata/struct/fail_field_type_mismatch.carbon b/toolchain/semantics/testdata/struct/fail_field_type_mismatch.carbon
index 8142e48a4920..ab6a8698ec09 100644
--- a/toolchain/semantics/testdata/struct/fail_field_type_mismatch.carbon
+++ b/toolchain/semantics/testdata/struct/fail_field_type_mismatch.carbon
@@ -59,5 +59,5 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/semantics/testdata/struct/fail_field_type_mismatch.carbon:[[@LINE+1]]:30: Cannot implicitly convert from `{.b: f64}` to `{.a: i32}`.
+// CHECK:STDERR: fail_field_type_mismatch.carbon:[[@LINE+1]]:30: Cannot implicitly convert from `{.b: f64}` to `{.a: i32}`.
 var x: {.a: i32} = {.b = 1.0};
diff --git a/toolchain/semantics/testdata/struct/fail_member_access_type.carbon b/toolchain/semantics/testdata/struct/fail_member_access_type.carbon
index ef4f9b98db83..74f551b2f8db 100644
--- a/toolchain/semantics/testdata/struct/fail_member_access_type.carbon
+++ b/toolchain/semantics/testdata/struct/fail_member_access_type.carbon
@@ -67,5 +67,5 @@
 // CHECK:STDOUT: ]
 
 var x: {.a: f64} = {.a = 4.0};
-// CHECK:STDERR: toolchain/semantics/testdata/struct/fail_member_access_type.carbon:[[@LINE+1]]:15: Type `{.a: f64}` does not have a member `b`.
+// CHECK:STDERR: fail_member_access_type.carbon:[[@LINE+1]]:15: Type `{.a: f64}` does not have a member `b`.
 var y: i32 = x.b;
diff --git a/toolchain/semantics/testdata/struct/fail_non_member_access.carbon b/toolchain/semantics/testdata/struct/fail_non_member_access.carbon
index 1d18c8728068..a7dde3b2a73e 100644
--- a/toolchain/semantics/testdata/struct/fail_non_member_access.carbon
+++ b/toolchain/semantics/testdata/struct/fail_non_member_access.carbon
@@ -67,5 +67,5 @@
 // CHECK:STDOUT: ]
 
 var x: {.a: i32} = {.a = 4};
-// CHECK:STDERR: toolchain/semantics/testdata/struct/fail_non_member_access.carbon:[[@LINE+1]]:15: Type `{.a: i32}` does not have a member `b`.
+// CHECK:STDERR: fail_non_member_access.carbon:[[@LINE+1]]:15: Type `{.a: i32}` does not have a member `b`.
 var y: i32 = x.b;
diff --git a/toolchain/semantics/testdata/struct/fail_too_few_values.carbon b/toolchain/semantics/testdata/struct/fail_too_few_values.carbon
index 83ce18c72b32..495869680a65 100644
--- a/toolchain/semantics/testdata/struct/fail_too_few_values.carbon
+++ b/toolchain/semantics/testdata/struct/fail_too_few_values.carbon
@@ -62,5 +62,5 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/semantics/testdata/struct/fail_too_few_values.carbon:[[@LINE+1]]:37: Cannot implicitly convert from `{.a: i32}` to `{.a: i32, .b: i32}`.
+// CHECK:STDERR: fail_too_few_values.carbon:[[@LINE+1]]:37: Cannot implicitly convert from `{.a: i32}` to `{.a: i32, .b: i32}`.
 var x: {.a: i32, .b: i32} = {.a = 1};
diff --git a/toolchain/semantics/testdata/struct/fail_type_assign.carbon b/toolchain/semantics/testdata/struct/fail_type_assign.carbon
index 15e54bc359ce..8b8904d66e75 100644
--- a/toolchain/semantics/testdata/struct/fail_type_assign.carbon
+++ b/toolchain/semantics/testdata/struct/fail_type_assign.carbon
@@ -49,5 +49,5 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/semantics/testdata/struct/fail_type_assign.carbon:[[@LINE+1]]:29: Cannot implicitly convert from `Type` to `{.a: i32}`.
+// CHECK:STDERR: fail_type_assign.carbon:[[@LINE+1]]:29: Cannot implicitly convert from `Type` to `{.a: i32}`.
 var x: {.a: i32} = {.a: i32};
diff --git a/toolchain/semantics/testdata/struct/fail_value_as_type.carbon b/toolchain/semantics/testdata/struct/fail_value_as_type.carbon
index 1e7ee601fec6..e54e4804cc5e 100644
--- a/toolchain/semantics/testdata/struct/fail_value_as_type.carbon
+++ b/toolchain/semantics/testdata/struct/fail_value_as_type.carbon
@@ -47,5 +47,5 @@
 // CHECK:STDOUT:   ],
 // CHECK:STDOUT: ]
 
-// CHECK:STDERR: toolchain/semantics/testdata/struct/fail_value_as_type.carbon:[[@LINE+1]]:15: Cannot implicitly convert from `{.a: i32}` to `Type`.
+// CHECK:STDERR: fail_value_as_type.carbon:[[@LINE+1]]:15: Cannot implicitly convert from `{.a: i32}` to `Type`.
 var x: {.a = 1};
diff --git a/toolchain/semantics/testdata/var/fail_duplicate_decl.carbon b/toolchain/semantics/testdata/var/fail_duplicate_decl.carbon
index 4de435507dcc..ea25017e30bd 100644
--- a/toolchain/semantics/testdata/var/fail_duplicate_decl.carbon
+++ b/toolchain/semantics/testdata/var/fail_duplicate_decl.carbon
@@ -53,7 +53,7 @@
 
 fn Main() {
   var x: i32 = 0;
-  // CHECK:STDERR: toolchain/semantics/testdata/var/fail_duplicate_decl.carbon:[[@LINE+2]]:7: Redefining x in the same scope.
-  // CHECK:STDERR: toolchain/semantics/testdata/var/fail_duplicate_decl.carbon:[[@LINE-2]]:7: Previous definition is here.
+  // CHECK:STDERR: fail_duplicate_decl.carbon:[[@LINE+2]]:7: Redefining x in the same scope.
+  // CHECK:STDERR: fail_duplicate_decl.carbon:[[@LINE-2]]:7: Previous definition is here.
   var x: i32 = 0;
 }
diff --git a/toolchain/semantics/testdata/var/fail_init_type_mismatch.carbon b/toolchain/semantics/testdata/var/fail_init_type_mismatch.carbon
index 32c730ea88bd..f402aa6bd510 100644
--- a/toolchain/semantics/testdata/var/fail_init_type_mismatch.carbon
+++ b/toolchain/semantics/testdata/var/fail_init_type_mismatch.carbon
@@ -42,6 +42,6 @@
 // CHECK:STDOUT: ]
 
 fn Main() {
-  // CHECK:STDERR: toolchain/semantics/testdata/var/fail_init_type_mismatch.carbon:[[@LINE+1]]:19: Cannot implicitly convert from `f64` to `i32`.
+  // CHECK:STDERR: fail_init_type_mismatch.carbon:[[@LINE+1]]:19: Cannot implicitly convert from `f64` to `i32`.
   var x: i32 = 1.0;
 }
diff --git a/toolchain/semantics/testdata/var/fail_init_with_self.carbon b/toolchain/semantics/testdata/var/fail_init_with_self.carbon
index 1a1c17fd9888..23fe0c349e1b 100644
--- a/toolchain/semantics/testdata/var/fail_init_with_self.carbon
+++ b/toolchain/semantics/testdata/var/fail_init_with_self.carbon
@@ -39,6 +39,6 @@
 // CHECK:STDOUT: ]
 
 fn Main() {
-  // CHECK:STDERR: toolchain/semantics/testdata/var/fail_init_with_self.carbon:[[@LINE+1]]:16: Name x not found
+  // CHECK:STDERR: fail_init_with_self.carbon:[[@LINE+1]]:16: Name x not found
   var x: i32 = x;
 }
diff --git a/toolchain/semantics/testdata/var/fail_lookup_outside_scope.carbon b/toolchain/semantics/testdata/var/fail_lookup_outside_scope.carbon
index 1b2768ec9ec6..184af77691c7 100644
--- a/toolchain/semantics/testdata/var/fail_lookup_outside_scope.carbon
+++ b/toolchain/semantics/testdata/var/fail_lookup_outside_scope.carbon
@@ -47,5 +47,5 @@ fn Main() {
   var x: i32;
 }
 
-// CHECK:STDERR: toolchain/semantics/testdata/var/fail_lookup_outside_scope.carbon:[[@LINE+1]]:14: Name x not found
+// CHECK:STDERR: fail_lookup_outside_scope.carbon:[[@LINE+1]]:14: Name x not found
 var y: i32 = x;
diff --git a/toolchain/semantics/testdata/var/fail_storage_is_literal.carbon b/toolchain/semantics/testdata/var/fail_storage_is_literal.carbon
index 5f8d808dfad4..9e88b8c69b0b 100644
--- a/toolchain/semantics/testdata/var/fail_storage_is_literal.carbon
+++ b/toolchain/semantics/testdata/var/fail_storage_is_literal.carbon
@@ -45,6 +45,6 @@
 // CHECK:STDOUT: ]
 
 fn Main() {
-  // CHECK:STDERR: toolchain/semantics/testdata/var/fail_storage_is_literal.carbon:[[@LINE+1]]:10: Cannot implicitly convert from `i32` to `Type`.
+  // CHECK:STDERR: fail_storage_is_literal.carbon:[[@LINE+1]]:10: Cannot implicitly convert from `i32` to `Type`.
   var x: 1 = 1;
 }