diff --git a/toolchain/lower/testdata/interop/cpp/reverse/class.carbon b/toolchain/lower/testdata/interop/cpp/class/export/class.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/reverse/class.carbon
rename to toolchain/lower/testdata/interop/cpp/class/export/class.carbon
index 59ce9543ffb4..af60f05668dc 100644
--- a/toolchain/lower/testdata/interop/cpp/reverse/class.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/export/class.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/lower/testdata/interop/cpp/reverse/class.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/class/export/class.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/reverse/class.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/class/export/class.carbon
 
 // --- pointer.carbon
 library "[[@TEST_NAME]]";
diff --git a/toolchain/lower/testdata/interop/cpp/reverse/mangle_type.carbon b/toolchain/lower/testdata/interop/cpp/class/export/mangle.carbon
similarity index 95%
rename from toolchain/lower/testdata/interop/cpp/reverse/mangle_type.carbon
rename to toolchain/lower/testdata/interop/cpp/class/export/mangle.carbon
index b9b77aa3bf4d..70020791bf2d 100644
--- a/toolchain/lower/testdata/interop/cpp/reverse/mangle_type.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/export/mangle.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/lower/testdata/interop/cpp/reverse/mangle_type.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/class/export/mangle.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/reverse/mangle_type.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/class/export/mangle.carbon
 
 // --- other.carbon
 package Other;
diff --git a/toolchain/lower/testdata/interop/cpp/reverse/method.carbon b/toolchain/lower/testdata/interop/cpp/class/export/method.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/reverse/method.carbon
rename to toolchain/lower/testdata/interop/cpp/class/export/method.carbon
index 9c4049034abe..5fc0bdca67ef 100644
--- a/toolchain/lower/testdata/interop/cpp/reverse/method.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/export/method.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/lower/testdata/interop/cpp/reverse/method.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/class/export/method.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/reverse/method.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/class/export/method.carbon
 
 // --- method.carbon
 library "[[@TEST_NAME]]";
diff --git a/toolchain/lower/testdata/interop/cpp/base.carbon b/toolchain/lower/testdata/interop/cpp/class/import/base.carbon
similarity index 98%
rename from toolchain/lower/testdata/interop/cpp/base.carbon
rename to toolchain/lower/testdata/interop/cpp/class/import/base.carbon
index 00b005ba4ba6..d26cedce5643 100644
--- a/toolchain/lower/testdata/interop/cpp/base.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/import/base.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/lower/testdata/interop/cpp/base.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/class/import/base.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/base.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/class/import/base.carbon
 
 // --- structs.h
 
diff --git a/toolchain/lower/testdata/interop/cpp/constructor.carbon b/toolchain/lower/testdata/interop/cpp/class/import/constructor.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/constructor.carbon
rename to toolchain/lower/testdata/interop/cpp/class/import/constructor.carbon
index 6ddb4b3728f5..3c2afc9b3fce 100644
--- a/toolchain/lower/testdata/interop/cpp/constructor.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/import/constructor.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/lower/testdata/interop/cpp/constructor.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/class/import/constructor.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/constructor.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/class/import/constructor.carbon
 
 // ============================================================================
 // Default constructor
diff --git a/toolchain/lower/testdata/interop/cpp/copy_vs_move.carbon b/toolchain/lower/testdata/interop/cpp/class/import/copy_vs_move.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/copy_vs_move.carbon
rename to toolchain/lower/testdata/interop/cpp/class/import/copy_vs_move.carbon
index 1c47445c2885..5866e8ee2092 100644
--- a/toolchain/lower/testdata/interop/cpp/copy_vs_move.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/import/copy_vs_move.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/lower/testdata/interop/cpp/copy_vs_move.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/class/import/copy_vs_move.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/copy_vs_move.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/class/import/copy_vs_move.carbon
 
 // --- copyable.carbon
 library "[[@TEST_NAME]]";
diff --git a/toolchain/lower/testdata/interop/cpp/field.carbon b/toolchain/lower/testdata/interop/cpp/class/import/field.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/field.carbon
rename to toolchain/lower/testdata/interop/cpp/class/import/field.carbon
index f394c0ac90fd..d6d1249161df 100644
--- a/toolchain/lower/testdata/interop/cpp/field.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/import/field.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/lower/testdata/interop/cpp/field.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/class/import/field.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/field.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/class/import/field.carbon
 
 // --- struct.h
 
diff --git a/toolchain/lower/testdata/interop/cpp/method.carbon b/toolchain/lower/testdata/interop/cpp/class/import/method.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/method.carbon
rename to toolchain/lower/testdata/interop/cpp/class/import/method.carbon
index 5022e9c5408e..d0b3b6ed875a 100644
--- a/toolchain/lower/testdata/interop/cpp/method.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/import/method.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/lower/testdata/interop/cpp/method.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/class/import/method.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/method.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/class/import/method.carbon
 
 // --- methods.h
 
diff --git a/toolchain/lower/testdata/interop/cpp/virtual_base.carbon b/toolchain/lower/testdata/interop/cpp/class/import/virtual_base.carbon
similarity index 98%
rename from toolchain/lower/testdata/interop/cpp/virtual_base.carbon
rename to toolchain/lower/testdata/interop/cpp/class/import/virtual_base.carbon
index 9727b60bae60..18ac2616a3a7 100644
--- a/toolchain/lower/testdata/interop/cpp/virtual_base.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/import/virtual_base.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/lower/testdata/interop/cpp/virtual_base.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/class/import/virtual_base.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/virtual_base.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/class/import/virtual_base.carbon
 
 // --- diamond.h
 
diff --git a/toolchain/lower/testdata/interop/cpp/reverse/function.carbon b/toolchain/lower/testdata/interop/cpp/function/export/function.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/reverse/function.carbon
rename to toolchain/lower/testdata/interop/cpp/function/export/function.carbon
index 7dc371ca1367..05e934f195b2 100644
--- a/toolchain/lower/testdata/interop/cpp/reverse/function.carbon
+++ b/toolchain/lower/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/lower/testdata/interop/cpp/reverse/function.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/function/export/function.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/reverse/function.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function/export/function.carbon
 
 // --- other.carbon
 package Other;
diff --git a/toolchain/lower/testdata/interop/cpp/cpp_run.carbon b/toolchain/lower/testdata/interop/cpp/function/import/cpp_run.carbon
similarity index 94%
rename from toolchain/lower/testdata/interop/cpp/cpp_run.carbon
rename to toolchain/lower/testdata/interop/cpp/function/import/cpp_run.carbon
index 265f94fa9d5e..cf6aec02e349 100644
--- a/toolchain/lower/testdata/interop/cpp/cpp_run.carbon
+++ b/toolchain/lower/testdata/interop/cpp/function/import/cpp_run.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/lower/testdata/interop/cpp/cpp_run.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/function/import/cpp_run.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/cpp_run.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function/import/cpp_run.carbon
 
 // --- carbon_run.carbon
 
diff --git a/toolchain/lower/testdata/interop/cpp/function_decl.carbon b/toolchain/lower/testdata/interop/cpp/function/import/function_decl.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/function_decl.carbon
rename to toolchain/lower/testdata/interop/cpp/function/import/function_decl.carbon
index 3aa42285e712..276b009627af 100644
--- a/toolchain/lower/testdata/interop/cpp/function_decl.carbon
+++ b/toolchain/lower/testdata/interop/cpp/function/import/function_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/lower/testdata/interop/cpp/function_decl.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/function/import/function_decl.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function_decl.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function/import/function_decl.carbon
 
 // ============================================================================
 // function_decl
diff --git a/toolchain/lower/testdata/interop/cpp/function_in_template.carbon b/toolchain/lower/testdata/interop/cpp/function/import/function_in_template.carbon
similarity index 94%
rename from toolchain/lower/testdata/interop/cpp/function_in_template.carbon
rename to toolchain/lower/testdata/interop/cpp/function/import/function_in_template.carbon
index 457cf90f1315..1b546ead3faa 100644
--- a/toolchain/lower/testdata/interop/cpp/function_in_template.carbon
+++ b/toolchain/lower/testdata/interop/cpp/function/import/function_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/lower/testdata/interop/cpp/function_in_template.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/function/import/function_in_template.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function_in_template.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function/import/function_in_template.carbon
 
 // --- class_template.h
 
diff --git a/toolchain/lower/testdata/interop/cpp/import_inline.carbon b/toolchain/lower/testdata/interop/cpp/function/import/import_inline.carbon
similarity index 96%
rename from toolchain/lower/testdata/interop/cpp/import_inline.carbon
rename to toolchain/lower/testdata/interop/cpp/function/import/import_inline.carbon
index 20a35ed8493e..3c01cf315903 100644
--- a/toolchain/lower/testdata/interop/cpp/import_inline.carbon
+++ b/toolchain/lower/testdata/interop/cpp/function/import/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/lower/testdata/interop/cpp/import_inline.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/function/import/import_inline.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/import_inline.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function/import/import_inline.carbon
 
 import Cpp inline '''
 
diff --git a/toolchain/lower/testdata/interop/cpp/parameters.carbon b/toolchain/lower/testdata/interop/cpp/function/import/parameters.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/parameters.carbon
rename to toolchain/lower/testdata/interop/cpp/function/import/parameters.carbon
index 07f421b9d8d9..74bbac56c895 100644
--- a/toolchain/lower/testdata/interop/cpp/parameters.carbon
+++ b/toolchain/lower/testdata/interop/cpp/function/import/parameters.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/lower/testdata/interop/cpp/parameters.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/function/import/parameters.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/parameters.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function/import/parameters.carbon
 
 // ============================================================================
 // Parameter requires a thunk to be generated
diff --git a/toolchain/lower/testdata/interop/cpp/return.carbon b/toolchain/lower/testdata/interop/cpp/function/import/return.carbon
similarity index 99%
rename from toolchain/lower/testdata/interop/cpp/return.carbon
rename to toolchain/lower/testdata/interop/cpp/function/import/return.carbon
index d142f6fa5d65..2c2079ab13ab 100644
--- a/toolchain/lower/testdata/interop/cpp/return.carbon
+++ b/toolchain/lower/testdata/interop/cpp/function/import/return.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/lower/testdata/interop/cpp/return.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/function/import/return.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/return.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/function/import/return.carbon
 
 // --- ints.h