test-refactor: add a helper for making it even easier to retest things

tests/selfvalidate_test.cxx

@@ -134,6 +134,15 @@ INSTANTIATE_TEST_SUITE_P(Draft2020_12, JsonSchema, SchemaTests(Version::Draft202
                          SchemaTestName);
 
 int main(int argc, char ** argv) {
+  using std::string_literals::operator""s;
+  if (argc != 4) {
+    // Skip down to normal GTest things...
+  } else if ("--suite"s == argv[1] || "--case"s == argv[1]) {
+    std::string arg1 = "--gtest_filter="s + argv[2];
+    std::string arg2 = "--json_"s + (argv[1] + 2) + "_filter="s + argv[3];
+    std::array<char *, 3> args{argv[0], &*arg1.begin(), &*arg2.begin()};
+    return main(args.size(), args.data());
+  }
   testing::InitGoogleMock(&argc, argv);
   return RUN_ALL_TESTS();
 }