diff --git a/toolchain/check/testdata/interop/cpp/bad_flags.carbon b/toolchain/check/testdata/interop/cpp/basics/bad_flags.carbon
similarity index 86%
rename from toolchain/check/testdata/interop/cpp/bad_flags.carbon
rename to toolchain/check/testdata/interop/cpp/basics/bad_flags.carbon
index 096b3f628a6a..0ab862dcc308 100644
--- a/toolchain/check/testdata/interop/cpp/bad_flags.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/bad_flags.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/bad_flags.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/bad_flags.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/bad_flags.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/bad_flags.carbon
 // CHECK:STDERR: error: unable to read PCH file does_not_exist.pch: 'No such file or directory' [CppInteropParseError]
 // CHECK:STDERR:
 // CHECK:STDERR: error: PCH file 'does_not_exist.pch' not found: module file not found [CppInteropParseError]
diff --git a/toolchain/check/testdata/interop/cpp/cpp_diagnostics.carbon b/toolchain/check/testdata/interop/cpp/basics/cpp_diagnostics.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/cpp_diagnostics.carbon
rename to toolchain/check/testdata/interop/cpp/basics/cpp_diagnostics.carbon
index ba2d8580ba08..7152fc5a9e33 100644
--- a/toolchain/check/testdata/interop/cpp/cpp_diagnostics.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/cpp_diagnostics.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/cpp_diagnostics.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/cpp_diagnostics.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/cpp_diagnostics.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/cpp_diagnostics.carbon
 
 // ============================================================================
 // One error
diff --git a/toolchain/check/testdata/interop/cpp/bad_import.carbon b/toolchain/check/testdata/interop/cpp/basics/import/bad_import.carbon
similarity index 96%
rename from toolchain/check/testdata/interop/cpp/bad_import.carbon
rename to toolchain/check/testdata/interop/cpp/basics/import/bad_import.carbon
index 7219feea84ba..d0ab023892ad 100644
--- a/toolchain/check/testdata/interop/cpp/bad_import.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/import/bad_import.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/bad_import.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/import/bad_import.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/bad_import.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/import/bad_import.carbon
 
 // --- fail_import_cpp_library_empty.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/cpp_namespace.carbon b/toolchain/check/testdata/interop/cpp/basics/import/cpp_namespace.carbon
similarity index 97%
rename from toolchain/check/testdata/interop/cpp/cpp_namespace.carbon
rename to toolchain/check/testdata/interop/cpp/basics/import/cpp_namespace.carbon
index 82a7aa8ed39a..22f7096fefe1 100644
--- a/toolchain/check/testdata/interop/cpp/cpp_namespace.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/import/cpp_namespace.carbon
@@ -8,9 +8,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/cpp_namespace.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/import/cpp_namespace.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/cpp_namespace.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/import/cpp_namespace.carbon
 
 // --- header.h
 
diff --git a/toolchain/check/testdata/interop/cpp/fail_fuzzing.carbon b/toolchain/check/testdata/interop/cpp/basics/import/fail_fuzzing.carbon
similarity index 83%
rename from toolchain/check/testdata/interop/cpp/fail_fuzzing.carbon
rename to toolchain/check/testdata/interop/cpp/basics/import/fail_fuzzing.carbon
index d4fe9c879a70..fa4c714bd70e 100644
--- a/toolchain/check/testdata/interop/cpp/fail_fuzzing.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/import/fail_fuzzing.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/fail_fuzzing.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/import/fail_fuzzing.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/fail_fuzzing.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/import/fail_fuzzing.carbon
 
 // CHECK:STDERR: fail_fuzzing.carbon:[[@LINE+4]]:1: error: `Cpp` import found during fuzzing [CppInteropFuzzing]
 // CHECK:STDERR: import Cpp library "file.h";
diff --git a/toolchain/check/testdata/interop/cpp/file_not_found.carbon b/toolchain/check/testdata/interop/cpp/basics/import/file_not_found.carbon
similarity index 82%
rename from toolchain/check/testdata/interop/cpp/file_not_found.carbon
rename to toolchain/check/testdata/interop/cpp/basics/import/file_not_found.carbon
index fdc1b5b5f14d..22e73899ccd6 100644
--- a/toolchain/check/testdata/interop/cpp/file_not_found.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/import/file_not_found.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/file_not_found.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/import/file_not_found.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/file_not_found.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/import/file_not_found.carbon
 
 // --- fail_cpp_file_not_found.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/import.carbon b/toolchain/check/testdata/interop/cpp/basics/import/import.carbon
similarity index 98%
rename from toolchain/check/testdata/interop/cpp/import.carbon
rename to toolchain/check/testdata/interop/cpp/basics/import/import.carbon
index dee8f2dd70cb..b1649ad95718 100644
--- a/toolchain/check/testdata/interop/cpp/import.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/import/import.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/import.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/import/import.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/import.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/import/import.carbon
 
 // ============================================================================
 // Import C++ namespace indirectly
diff --git a/toolchain/check/testdata/interop/cpp/include.carbon b/toolchain/check/testdata/interop/cpp/basics/import/include.carbon
similarity index 85%
rename from toolchain/check/testdata/interop/cpp/include.carbon
rename to toolchain/check/testdata/interop/cpp/basics/import/include.carbon
index 66595f121256..e360785402dc 100644
--- a/toolchain/check/testdata/interop/cpp/include.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/import/include.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/include.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/import/include.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/include.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/import/include.carbon
 
 // --- included_file.h
 
diff --git a/toolchain/check/testdata/interop/cpp/include_paths.carbon b/toolchain/check/testdata/interop/cpp/basics/import/include_paths.carbon
similarity index 85%
rename from toolchain/check/testdata/interop/cpp/include_paths.carbon
rename to toolchain/check/testdata/interop/cpp/basics/import/include_paths.carbon
index 6557639718f6..d201548d2266 100644
--- a/toolchain/check/testdata/interop/cpp/include_paths.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/import/include_paths.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/include_paths.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/import/include_paths.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/include_paths.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/import/include_paths.carbon
 
 // --- include_stddef.h
 
diff --git a/toolchain/check/testdata/interop/cpp/multiple_imports.carbon b/toolchain/check/testdata/interop/cpp/basics/import/multiple_imports.carbon
similarity index 84%
rename from toolchain/check/testdata/interop/cpp/multiple_imports.carbon
rename to toolchain/check/testdata/interop/cpp/basics/import/multiple_imports.carbon
index 2f36fa7b0769..14f919fac4b1 100644
--- a/toolchain/check/testdata/interop/cpp/multiple_imports.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/import/multiple_imports.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/multiple_imports.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/import/multiple_imports.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/multiple_imports.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/import/multiple_imports.carbon
 
 // --- file1.h
 
diff --git a/toolchain/check/testdata/interop/cpp/inline_decl.carbon b/toolchain/check/testdata/interop/cpp/basics/inline/decl.carbon
similarity index 96%
rename from toolchain/check/testdata/interop/cpp/inline_decl.carbon
rename to toolchain/check/testdata/interop/cpp/basics/inline/decl.carbon
index f417303c551d..96dbe7597629 100644
--- a/toolchain/check/testdata/interop/cpp/inline_decl.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/inline/decl.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/inline_decl.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/inline/decl.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/inline_decl.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/inline/decl.carbon
 
 // --- inline_decl.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/inline.carbon b/toolchain/check/testdata/interop/cpp/basics/inline/import.carbon
similarity index 96%
rename from toolchain/check/testdata/interop/cpp/inline.carbon
rename to toolchain/check/testdata/interop/cpp/basics/inline/import.carbon
index e8bb7ca7b311..5c574872b584 100644
--- a/toolchain/check/testdata/interop/cpp/inline.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/inline/import.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/inline.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/inline/import.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/inline.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/inline/import.carbon
 
 // --- use_inline_function_decl.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/modules.carbon b/toolchain/check/testdata/interop/cpp/basics/inline/modules.carbon
similarity index 95%
rename from toolchain/check/testdata/interop/cpp/modules.carbon
rename to toolchain/check/testdata/interop/cpp/basics/inline/modules.carbon
index 4d52d6e13f72..d0ce04f26983 100644
--- a/toolchain/check/testdata/interop/cpp/modules.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/inline/modules.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/modules.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/inline/modules.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/modules.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/inline/modules.carbon
 
 // --- fail_export_module_in_inline_cpp.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/unsupported_decl_type.carbon b/toolchain/check/testdata/interop/cpp/basics/unsupported_decl_type.carbon
similarity index 92%
rename from toolchain/check/testdata/interop/cpp/unsupported_decl_type.carbon
rename to toolchain/check/testdata/interop/cpp/basics/unsupported_decl_type.carbon
index 18d2066a89f4..a2e284bdda8b 100644
--- a/toolchain/check/testdata/interop/cpp/unsupported_decl_type.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/unsupported_decl_type.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/unsupported_decl_type.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/unsupported_decl_type.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/unsupported_decl_type.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/unsupported_decl_type.carbon
 
 // --- structured_binding.h
 
diff --git a/toolchain/check/testdata/interop/cpp/unused_internal.carbon b/toolchain/check/testdata/interop/cpp/basics/unused_internal.carbon
similarity index 88%
rename from toolchain/check/testdata/interop/cpp/unused_internal.carbon
rename to toolchain/check/testdata/interop/cpp/basics/unused_internal.carbon
index 9b94930b95b6..27c40a5ec7da 100644
--- a/toolchain/check/testdata/interop/cpp/unused_internal.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/unused_internal.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/unused_internal.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/basics/unused_internal.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/unused_internal.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/basics/unused_internal.carbon
 
 // --- unused.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/reverse/function.carbon b/toolchain/check/testdata/interop/cpp/function/export/function.carbon
similarity index 95%
rename from toolchain/check/testdata/interop/cpp/reverse/function.carbon
rename to toolchain/check/testdata/interop/cpp/function/export/function.carbon
index a11b40e72588..994ac1b663a1 100644
--- a/toolchain/check/testdata/interop/cpp/reverse/function.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/export/function.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/reverse/function.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/export/function.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/reverse/function.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/export/function.carbon
 
 // --- other.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/reverse/thunk_ast.carbon b/toolchain/check/testdata/interop/cpp/function/export/thunk_ast.carbon
similarity index 95%
rename from toolchain/check/testdata/interop/cpp/reverse/thunk_ast.carbon
rename to toolchain/check/testdata/interop/cpp/function/export/thunk_ast.carbon
index 4eee7c28525d..b233524790d7 100644
--- a/toolchain/check/testdata/interop/cpp/reverse/thunk_ast.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/export/thunk_ast.carbon
@@ -8,9 +8,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/reverse/thunk_ast.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/export/thunk_ast.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/reverse/thunk_ast.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/export/thunk_ast.carbon
 // CHECK:STDOUT: TranslationUnitDecl {{0x[a-f0-9]+}} <<invalid sloc>> <invalid sloc>
 // CHECK:STDOUT: |-NamespaceDecl {{0x[a-f0-9]+}} <<invalid sloc>> <invalid sloc> Carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/function/arithmetic_types_bridged.carbon b/toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_bridged.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/arithmetic_types_bridged.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_bridged.carbon
index 21a62ee2fd65..c6f21f0e38ca 100644
--- a/toolchain/check/testdata/interop/cpp/function/arithmetic_types_bridged.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_bridged.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/arithmetic_types_bridged.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_bridged.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/arithmetic_types_bridged.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_bridged.carbon
 
 // Tests for the case where we need a thunk when calling a C++ function from
 // Carbon, because the parameter and return types might have a non-trivial
diff --git a/toolchain/check/testdata/interop/cpp/function/arithmetic_types_direct.carbon b/toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_direct.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/arithmetic_types_direct.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_direct.carbon
index de862af6d4fb..a8543d81f0a6 100644
--- a/toolchain/check/testdata/interop/cpp/function/arithmetic_types_direct.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_direct.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/arithmetic_types_direct.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_direct.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/arithmetic_types_direct.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/arithmetic_types_direct.carbon
 
 // Tests for the case where we can directly call a C++ function from Carbon,
 // because the parameter and return types are known to have a sufficiently
diff --git a/toolchain/check/testdata/interop/cpp/function/class.carbon b/toolchain/check/testdata/interop/cpp/function/import/class.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/class.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/class.carbon
index 5d0a0e9464a8..c62c5f05fec9 100644
--- a/toolchain/check/testdata/interop/cpp/function/class.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/class.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/class.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/class.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/class.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/class.carbon
 
 // ============================================================================
 // Forward-declared class as parameter type
diff --git a/toolchain/check/testdata/interop/cpp/constexpr.carbon b/toolchain/check/testdata/interop/cpp/function/import/constexpr.carbon
similarity index 79%
rename from toolchain/check/testdata/interop/cpp/constexpr.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/constexpr.carbon
index 4e317d92e756..e1779468f9dd 100644
--- a/toolchain/check/testdata/interop/cpp/constexpr.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/constexpr.carbon
@@ -7,60 +7,11 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/constexpr.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/constexpr.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/constexpr.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/constexpr.carbon
 
-// --- bool.carbon
-
-library "[[@TEST_NAME]]";
-
-import Cpp inline '''
-constexpr bool b = true;
-''';
-
-class C(B:! bool) {}
-fn F() -> C(Cpp.b);
-let x: C(true) = F();
-
-// --- int.carbon
-
-library "[[@TEST_NAME]]";
-
-import Cpp inline '''
-constexpr int i = 123;
-''';
-
-class C(I:! i32) {}
-fn F() -> C(Cpp.i);
-let x: C(123) = F();
-
-// --- float.carbon
-
-library "[[@TEST_NAME]]";
-
-import Cpp inline '''
-constexpr float flt = 123.5;
-''';
-
-class C(V:! f32) {}
-fn F() -> C(Cpp.flt);
-let x: C(123.5) = F();
-
-// --- pointer.carbon
-
-library "[[@TEST_NAME]]";
-
-import Cpp inline '''
-int i = 123;
-constexpr int* _Nonnull ptr = &i;
-''';
-
-class C(V:! i32*) {}
-fn F() -> C(Cpp.ptr);
-let x: C(&Cpp.i) = F();
-
-// --- function.carbon
+// --- basic.carbon
 
 library "[[@TEST_NAME]]";
 
@@ -70,7 +21,7 @@ constexpr int f(int a, int b) { return a + b; }
 
 let a: array(i32, Cpp.f(1, 2)) = (1, 2, 3);
 
-// --- function_bool_param.carbon
+// --- bool_param.carbon
 
 library "[[@TEST_NAME]]";
 
@@ -82,7 +33,7 @@ constexpr int f(bool b) {
 
 let a: array(i32, Cpp.f(true)) = (1, 2, 3);
 
-// --- function_float_param.carbon
+// --- float_param.carbon
 
 library "[[@TEST_NAME]]";
 
@@ -94,7 +45,7 @@ constexpr int f(float b) {
 
 let a: array(i32, Cpp.f(3.0)) = (1, 2, 3);
 
-// --- function_return_bool.carbon
+// --- return_bool.carbon
 
 library "[[@TEST_NAME]]";
 
diff --git a/toolchain/check/testdata/interop/cpp/function/decayed_param.carbon b/toolchain/check/testdata/interop/cpp/function/import/decayed_param.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/decayed_param.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/decayed_param.carbon
index 05aeb31c5f17..01f4618b9cbb 100644
--- a/toolchain/check/testdata/interop/cpp/function/decayed_param.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/decayed_param.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/decayed_param.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/decayed_param.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/decayed_param.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/decayed_param.carbon
 
 // --- params.h
 
diff --git a/toolchain/check/testdata/interop/cpp/function/default_arg.carbon b/toolchain/check/testdata/interop/cpp/function/import/default_arg.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/default_arg.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/default_arg.carbon
index a4629bf0cbef..4c6b6c928f3a 100644
--- a/toolchain/check/testdata/interop/cpp/function/default_arg.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/default_arg.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/default_arg.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/default_arg.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/default_arg.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/default_arg.carbon
 
 // --- functions.h
 
diff --git a/toolchain/check/testdata/interop/cpp/function/extern_c.carbon b/toolchain/check/testdata/interop/cpp/function/import/extern_c.carbon
similarity index 98%
rename from toolchain/check/testdata/interop/cpp/function/extern_c.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/extern_c.carbon
index fec1421e7023..8b37cca15517 100644
--- a/toolchain/check/testdata/interop/cpp/function/extern_c.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/extern_c.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/extern_c.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/extern_c.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/extern_c.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/extern_c.carbon
 
 // --- extern_c_function.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/function/full_semir.carbon b/toolchain/check/testdata/interop/cpp/function/import/full_semir.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/full_semir.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/full_semir.carbon
index 8249b21ada02..d50e7479e9df 100644
--- a/toolchain/check/testdata/interop/cpp/function/full_semir.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/full_semir.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/full_semir.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/full_semir.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/full_semir.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/full_semir.carbon
 
 // ============================================================================
 // Function with short parameter
diff --git a/toolchain/check/testdata/interop/cpp/function/function.carbon b/toolchain/check/testdata/interop/cpp/function/import/function.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/function.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/function.carbon
index 276c102080f4..7a7fcafa5696 100644
--- a/toolchain/check/testdata/interop/cpp/function/function.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/function.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/function.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/function.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/function.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/function.carbon
 
 // ============================================================================
 // Global
diff --git a/toolchain/check/testdata/interop/cpp/function/in_template.carbon b/toolchain/check/testdata/interop/cpp/function/import/in_template.carbon
similarity index 97%
rename from toolchain/check/testdata/interop/cpp/function/in_template.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/in_template.carbon
index 3f93791e1e03..e8296cbf6a00 100644
--- a/toolchain/check/testdata/interop/cpp/function/in_template.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/in_template.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/in_template.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/in_template.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/in_template.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/in_template.carbon
 
 // --- class_template.h
 
diff --git a/toolchain/check/testdata/interop/cpp/function/inline.carbon b/toolchain/check/testdata/interop/cpp/function/import/inline.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/inline.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/inline.carbon
index 8d199d312b6b..e3355b87a989 100644
--- a/toolchain/check/testdata/interop/cpp/function/inline.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/inline.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/inline.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/inline.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/inline.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/inline.carbon
 
 // ============================================================================
 // With definition
diff --git a/toolchain/check/testdata/interop/cpp/function/multiple_too_few_args_calls.carbon b/toolchain/check/testdata/interop/cpp/function/import/multiple_too_few_args_calls.carbon
similarity index 94%
rename from toolchain/check/testdata/interop/cpp/function/multiple_too_few_args_calls.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/multiple_too_few_args_calls.carbon
index d26efd11f0b5..32fc26d17b8e 100644
--- a/toolchain/check/testdata/interop/cpp/function/multiple_too_few_args_calls.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/multiple_too_few_args_calls.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/multiple_too_few_args_calls.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/multiple_too_few_args_calls.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/multiple_too_few_args_calls.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/multiple_too_few_args_calls.carbon
 
 // --- fail_call_too_few_args.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/function/overloads.carbon b/toolchain/check/testdata/interop/cpp/function/import/overloads.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/overloads.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/overloads.carbon
index 5d7ec58a58a0..aae611fd9234 100644
--- a/toolchain/check/testdata/interop/cpp/function/overloads.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/overloads.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/overloads.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/overloads.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/overloads.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/overloads.carbon
 
 // ============================================================================
 // Overloaded sets tests
diff --git a/toolchain/check/testdata/interop/cpp/function/param_unsupported.carbon b/toolchain/check/testdata/interop/cpp/function/import/param_unsupported.carbon
similarity index 97%
rename from toolchain/check/testdata/interop/cpp/function/param_unsupported.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/param_unsupported.carbon
index d0b5b7389364..c2e5a4d6bc08 100644
--- a/toolchain/check/testdata/interop/cpp/function/param_unsupported.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/param_unsupported.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/param_unsupported.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/param_unsupported.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/param_unsupported.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/param_unsupported.carbon
 
 // ============================================================================
 // Unsupported primitive type
diff --git a/toolchain/check/testdata/interop/cpp/function/pointer.carbon b/toolchain/check/testdata/interop/cpp/function/import/pointer.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/pointer.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/pointer.carbon
index 3145008d759e..e4edeae5d255 100644
--- a/toolchain/check/testdata/interop/cpp/function/pointer.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/pointer.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/pointer.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/pointer.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/pointer.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/pointer.carbon
 
 // ============================================================================
 // Non-nullable pointer as a parameter type
diff --git a/toolchain/check/testdata/interop/cpp/function/qualified_param.carbon b/toolchain/check/testdata/interop/cpp/function/import/qualified_param.carbon
similarity index 98%
rename from toolchain/check/testdata/interop/cpp/function/qualified_param.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/qualified_param.carbon
index 766544eefb7f..fb0afbdb2343 100644
--- a/toolchain/check/testdata/interop/cpp/function/qualified_param.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/qualified_param.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/qualified_param.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/qualified_param.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/qualified_param.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/qualified_param.carbon
 
 // --- qualifiers.h
 
diff --git a/toolchain/check/testdata/interop/cpp/function/reference.carbon b/toolchain/check/testdata/interop/cpp/function/import/reference.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/reference.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/reference.carbon
index fe278b5a890e..8d5f23dc55a5 100644
--- a/toolchain/check/testdata/interop/cpp/function/reference.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/reference.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/reference.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/reference.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/reference.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/reference.carbon
 
 // ============================================================================
 // Lvalue reference as a parameter type
diff --git a/toolchain/check/testdata/interop/cpp/function/return.carbon b/toolchain/check/testdata/interop/cpp/function/import/return.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/return.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/return.carbon
index a3d4d11505de..e732c2711ed9 100644
--- a/toolchain/check/testdata/interop/cpp/function/return.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/return.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/return.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/return.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/return.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/return.carbon
 
 // ============================================================================
 // Multiple function with a return value
diff --git a/toolchain/check/testdata/interop/cpp/function/struct.carbon b/toolchain/check/testdata/interop/cpp/function/import/struct.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/struct.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/struct.carbon
index 3483557a0ff5..74389332d291 100644
--- a/toolchain/check/testdata/interop/cpp/function/struct.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/struct.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/struct.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/struct.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/struct.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/struct.carbon
 
 // ============================================================================
 // Forward-declared struct as parameter type
diff --git a/toolchain/check/testdata/interop/cpp/function/template.carbon b/toolchain/check/testdata/interop/cpp/function/import/template.carbon
similarity index 95%
rename from toolchain/check/testdata/interop/cpp/function/template.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/template.carbon
index 6a360d5920bf..c74e5be79024 100644
--- a/toolchain/check/testdata/interop/cpp/function/template.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/template.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/template.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/template.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/template.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/template.carbon
 
 // --- deduced_or_explicit.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/function/thunk_ast.carbon b/toolchain/check/testdata/interop/cpp/function/import/thunk_ast.carbon
similarity index 96%
rename from toolchain/check/testdata/interop/cpp/function/thunk_ast.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/thunk_ast.carbon
index 19bd32ad3a4f..c7d7db7e452a 100644
--- a/toolchain/check/testdata/interop/cpp/function/thunk_ast.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/thunk_ast.carbon
@@ -8,9 +8,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/thunk_ast.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/thunk_ast.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/thunk_ast.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/thunk_ast.carbon
 // CHECK:STDOUT: TranslationUnitDecl {{0x[a-f0-9]+}} <<invalid sloc>> <invalid sloc>
 // CHECK:STDOUT: |-NamespaceDecl {{0x[a-f0-9]+}} <<invalid sloc>> <invalid sloc> Carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/function/thunk_cpp26.carbon b/toolchain/check/testdata/interop/cpp/function/import/thunk_cpp26.carbon
similarity index 83%
rename from toolchain/check/testdata/interop/cpp/function/thunk_cpp26.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/thunk_cpp26.carbon
index dad0bd7b2c2f..0345a8b3266d 100644
--- a/toolchain/check/testdata/interop/cpp/function/thunk_cpp26.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/thunk_cpp26.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/thunk_cpp26.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/thunk_cpp26.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/thunk_cpp26.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/thunk_cpp26.carbon
 
 // --- thunk_required.h
 
diff --git a/toolchain/check/testdata/interop/cpp/function/union.carbon b/toolchain/check/testdata/interop/cpp/function/import/union.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/union.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/union.carbon
index 8abe21fbb26d..131b5131899f 100644
--- a/toolchain/check/testdata/interop/cpp/function/union.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/union.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/union.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/union.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/union.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/union.carbon
 
 // ============================================================================
 // Forward-declared union as parameter type
diff --git a/toolchain/check/testdata/interop/cpp/function/variadic.carbon b/toolchain/check/testdata/interop/cpp/function/import/variadic.carbon
similarity index 98%
rename from toolchain/check/testdata/interop/cpp/function/variadic.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/variadic.carbon
index 314c151695dc..aa85d5b3934d 100644
--- a/toolchain/check/testdata/interop/cpp/function/variadic.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/variadic.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/variadic.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/variadic.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/variadic.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/variadic.carbon
 
 // --- variadic.h
 
diff --git a/toolchain/check/testdata/interop/cpp/function/void_pointer.carbon b/toolchain/check/testdata/interop/cpp/function/import/void_pointer.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/void_pointer.carbon
rename to toolchain/check/testdata/interop/cpp/function/import/void_pointer.carbon
index 69a1ea9f0a85..5871fd06b666 100644
--- a/toolchain/check/testdata/interop/cpp/function/void_pointer.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/import/void_pointer.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/void_pointer.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/import/void_pointer.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/void_pointer.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/import/void_pointer.carbon
 
 // --- non_nullable_param.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/macros.carbon b/toolchain/check/testdata/interop/cpp/macros/macros.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/macros.carbon
rename to toolchain/check/testdata/interop/cpp/macros/macros.carbon
index f907cb93a235..c9282b8954c9 100644
--- a/toolchain/check/testdata/interop/cpp/macros.carbon
+++ b/toolchain/check/testdata/interop/cpp/macros/macros.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/macros.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/macros/macros.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/macros.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/macros/macros.carbon
 
 // ============================================================================
 // object-like macros
diff --git a/toolchain/check/testdata/interop/cpp/namespace/export.carbon b/toolchain/check/testdata/interop/cpp/namespace/export.carbon
index 20654e439307..4ead808fc749 100644
--- a/toolchain/check/testdata/interop/cpp/namespace/export.carbon
+++ b/toolchain/check/testdata/interop/cpp/namespace/export.carbon
@@ -10,6 +10,33 @@
 // TIP: To dump output, run:
 // TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/namespace/export.carbon
 
+// --- other.carbon
+package Other;
+namespace Nested;
+namespace Nested.Again;
+
+class Class1;
+// --- namespace.carbon
+
+library "[[@TEST_NAME]]";
+
+import Other;
+import Cpp inline '''
+namespace X = Carbon::Other;
+namespace Y = Carbon::Other::Nested;
+namespace Z = Carbon::Other::Nested::Again;
+Carbon::Other::Class1 *glbl;
+
+template<typename T> void f1() {
+  T* v;
+}
+
+void f2() {
+  f1<Carbon::Other::Class1>();
+}
+
+''';
+
 // --- alias_identity.carbon
 
 import Cpp;
diff --git a/toolchain/check/testdata/interop/cpp/deref.carbon b/toolchain/check/testdata/interop/cpp/operators/deref.carbon
similarity index 98%
rename from toolchain/check/testdata/interop/cpp/deref.carbon
rename to toolchain/check/testdata/interop/cpp/operators/deref.carbon
index 1b316d1826d5..87dbd3087763 100644
--- a/toolchain/check/testdata/interop/cpp/deref.carbon
+++ b/toolchain/check/testdata/interop/cpp/operators/deref.carbon
@@ -8,9 +8,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/deref.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/operators/deref.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/deref.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/operators/deref.carbon
 
 // --- const_deref.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/function/operators.carbon b/toolchain/check/testdata/interop/cpp/operators/operators.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/function/operators.carbon
rename to toolchain/check/testdata/interop/cpp/operators/operators.carbon
index cde851266ba8..55d493fc05fc 100644
--- a/toolchain/check/testdata/interop/cpp/function/operators.carbon
+++ b/toolchain/check/testdata/interop/cpp/operators/operators.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/operators.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/operators/operators.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/operators.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/operators/operators.carbon
 
 // ============================================================================
 // Unary operators
diff --git a/toolchain/check/testdata/interop/cpp/builtins.carbon b/toolchain/check/testdata/interop/cpp/primitive_types/arithmetic.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/builtins.carbon
rename to toolchain/check/testdata/interop/cpp/primitive_types/arithmetic.carbon
index b983ea275442..6dbd863ed0a7 100644
--- a/toolchain/check/testdata/interop/cpp/builtins.carbon
+++ b/toolchain/check/testdata/interop/cpp/primitive_types/arithmetic.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/builtins.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/primitive_types/arithmetic.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/builtins.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/primitive_types/arithmetic.carbon
 
 // --- supported_types.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/fail_todo_arithmetic_types_unmapped.carbon b/toolchain/check/testdata/interop/cpp/primitive_types/fail_todo_arithmetic_types_unmapped.carbon
similarity index 82%
rename from toolchain/check/testdata/interop/cpp/fail_todo_arithmetic_types_unmapped.carbon
rename to toolchain/check/testdata/interop/cpp/primitive_types/fail_todo_arithmetic_types_unmapped.carbon
index a6a054368230..34d147be63a0 100644
--- a/toolchain/check/testdata/interop/cpp/fail_todo_arithmetic_types_unmapped.carbon
+++ b/toolchain/check/testdata/interop/cpp/primitive_types/fail_todo_arithmetic_types_unmapped.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/fail_todo_arithmetic_types_unmapped.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/primitive_types/fail_todo_arithmetic_types_unmapped.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/fail_todo_arithmetic_types_unmapped.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/primitive_types/fail_todo_arithmetic_types_unmapped.carbon
 
 // Ensure we get a diagnostic when using a type that doesn't yet have a mapping
 // from C++ to Carbon.
diff --git a/toolchain/check/testdata/interop/cpp/builtins.llp64.carbon b/toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.llp64.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/builtins.llp64.carbon
rename to toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.llp64.carbon
index 75ad51d0e022..80f591708169 100644
--- a/toolchain/check/testdata/interop/cpp/builtins.llp64.carbon
+++ b/toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.llp64.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/builtins.llp64.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.llp64.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/builtins.llp64.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.llp64.carbon
 
 // --- long_long.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/builtins.lp64.carbon b/toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.lp64.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/builtins.lp64.carbon
rename to toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.lp64.carbon
index b1791e5eb885..447e7ea1388c 100644
--- a/toolchain/check/testdata/interop/cpp/builtins.lp64.carbon
+++ b/toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.lp64.carbon
@@ -7,9 +7,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/builtins.lp64.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.lp64.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/builtins.lp64.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/primitive_types/long_and_long_long.lp64.carbon
 
 // --- long.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/void.carbon b/toolchain/check/testdata/interop/cpp/primitive_types/void.carbon
similarity index 94%
rename from toolchain/check/testdata/interop/cpp/void.carbon
rename to toolchain/check/testdata/interop/cpp/primitive_types/void.carbon
index 1d6e38e5b713..3b2ac73a372b 100644
--- a/toolchain/check/testdata/interop/cpp/void.carbon
+++ b/toolchain/check/testdata/interop/cpp/primitive_types/void.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/void.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/primitive_types/void.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/void.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/primitive_types/void.carbon
 
 // --- void_not_incomplete.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/void_pointer.carbon b/toolchain/check/testdata/interop/cpp/primitive_types/void_pointer.carbon
similarity index 99%
rename from toolchain/check/testdata/interop/cpp/void_pointer.carbon
rename to toolchain/check/testdata/interop/cpp/primitive_types/void_pointer.carbon
index 5a38792e2a9d..4a14628d404b 100644
--- a/toolchain/check/testdata/interop/cpp/void_pointer.carbon
+++ b/toolchain/check/testdata/interop/cpp/primitive_types/void_pointer.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/void_pointer.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/primitive_types/void_pointer.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/void_pointer.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/primitive_types/void_pointer.carbon
 
 // --- implicit_as_from_cpp_class_pointer_to_void_pointer.carbon
 
diff --git a/toolchain/check/testdata/interop/cpp/reverse/simple.carbon b/toolchain/check/testdata/interop/cpp/reverse/simple.carbon
deleted file mode 100644
index a6dcca482860..000000000000
--- a/toolchain/check/testdata/interop/cpp/reverse/simple.carbon
+++ /dev/null
@@ -1,38 +0,0 @@
-// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-// Exceptions. See /LICENSE for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/none.carbon
-//
-// AUTOUPDATE
-// TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/reverse/simple.carbon
-// TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/reverse/simple.carbon
-
-// --- other.carbon
-package Other;
-namespace Nested;
-namespace Nested.Again;
-
-class Class1;
-// --- namespace.carbon
-
-library "[[@TEST_NAME]]";
-
-import Other;
-import Cpp inline '''
-namespace X = Carbon::Other;
-namespace Y = Carbon::Other::Nested;
-namespace Z = Carbon::Other::Nested::Again;
-Carbon::Other::Class1 *glbl;
-
-template<typename T> void f1() {
-  T* v;
-}
-
-void f2() {
-  f1<Carbon::Other::Class1>();
-}
-
-''';
diff --git a/toolchain/check/testdata/interop/cpp/var/constexpr.carbon b/toolchain/check/testdata/interop/cpp/var/constexpr.carbon
new file mode 100644
index 000000000000..f313eb26f905
--- /dev/null
+++ b/toolchain/check/testdata/interop/cpp/var/constexpr.carbon
@@ -0,0 +1,61 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/full.carbon
+// EXTRA-ARGS: --clang-arg=--std=c++20
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/var/constexpr.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/var/constexpr.carbon
+
+// --- bool.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp inline '''
+constexpr bool b = true;
+''';
+
+class C(B:! bool) {}
+fn F() -> C(Cpp.b);
+let x: C(true) = F();
+
+// --- int.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp inline '''
+constexpr int i = 123;
+''';
+
+class C(I:! i32) {}
+fn F() -> C(Cpp.i);
+let x: C(123) = F();
+
+// --- float.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp inline '''
+constexpr float flt = 123.5;
+''';
+
+class C(V:! f32) {}
+fn F() -> C(Cpp.flt);
+let x: C(123.5) = F();
+
+// --- pointer.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp inline '''
+int i = 123;
+constexpr int* _Nonnull ptr = &i;
+''';
+
+class C(V:! i32*) {}
+fn F() -> C(Cpp.ptr);
+let x: C(&Cpp.i) = F();