Fix windows-only issue in our compiler unittests.

Closes #16026

PiperOrigin-RevId: 617333656

src/google/protobuf/compiler/mock_code_generator.cc

@@ -50,6 +50,7 @@
 namespace google {
 namespace protobuf {
 namespace compiler {
+namespace {
 
 // Returns the list of the names of files in all_files in the form of a
 // comma-separated string.
@@ -71,14 +72,20 @@ static constexpr absl::string_view kFirstInsertionPoint =
 static constexpr absl::string_view kSecondInsertionPoint =
     "  # @@protoc_insertion_point(second_mock_insertion_point) is here\n";
 
-MockCodeGenerator::MockCodeGenerator(absl::string_view name) : name_(name) {
+absl::string_view GetTestCase() {
   const char* c_key = getenv("TEST_CASE");
   if (c_key == nullptr) {
     // In Windows, setting 'TEST_CASE=' is equivalent to unsetting
     // and therefore c_key can be nullptr
-    c_key = "";
+    return "";
   }
-  absl::string_view key(c_key);
+  return c_key;
+}
+
+}  // namespace
+
+MockCodeGenerator::MockCodeGenerator(absl::string_view name) : name_(name) {
+  absl::string_view key = GetTestCase();
   if (key == "no_editions") {
     suppressed_features_ |= CodeGenerator::FEATURE_SUPPORTS_EDITIONS;
   } else if (key == "invalid_features") {
@@ -214,7 +221,7 @@ bool MockCodeGenerator::Generate(const FileDescriptor* file,
                                  std::string* error) const {
   // Override minimum/maximum after generating the pool to simulate a plugin
   // that "works" but doesn't advertise support of the current edition.
-  absl::string_view test_case = getenv("TEST_CASE");
+  absl::string_view test_case = GetTestCase();
   if (test_case == "high_minimum") {
     minimum_edition_ = Edition::EDITION_99997_TEST_ONLY;
   } else if (test_case == "low_maximum") {