diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 030dcf219..f0758326f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -53,7 +53,6 @@ jobs:
           DART_VERSION="${{ steps.setup-dart.outputs.dart-version }}"
           if [[ "$DART_VERSION" =~ ^3 ]]; then
             ./tool/delete_dart_2_only_files.sh
-            ./tool/update_tests_for_dart_3.sh
             # Stage these changes so they don't show up in the generated file `git diff` check below
             git add .
           fi
@@ -146,7 +145,6 @@ jobs:
           DART_VERSION="${{ steps.setup-dart.outputs.dart-version }}"
           if [[ "$DART_VERSION" =~ ^3 ]]; then
             ./tool/delete_dart_2_only_files.sh
-            ./tool/update_tests_for_dart_3.sh
           fi
 
       - name: Analyze package source
@@ -196,7 +194,7 @@ jobs:
         run: |
           DART_VERSION="${{ steps.setup-dart.outputs.dart-version }}"
           if [[ "$DART_VERSION" =~ ^3 ]]; then
-            (cd ../.. && ./tool/delete_dart_2_only_files.sh && ./tool/update_tests_for_dart_3.sh)
+            (cd ../.. && ./tool/delete_dart_2_only_files.sh)
           fi
 
       - name: Validate dependencies
diff --git a/test/vm_tests/builder/over_react_builder_test.dart b/test/vm_tests/builder/over_react_builder_test.dart
index 48c96b624..bc195a6da 100644
--- a/test/vm_tests/builder/over_react_builder_test.dart
+++ b/test/vm_tests/builder/over_react_builder_test.dart
@@ -13,199 +13,199 @@
 // limitations under the License.
 
 @TestOn('vm')
-import 'dart:async';
 import 'dart:io';
 
-import 'package:build/build.dart';
-import 'package:build_resolvers/build_resolvers.dart';
-import 'package:build_test/build_test.dart';
-import 'package:collection/collection.dart' show IterableExtension;
-import 'package:logging/logging.dart';
-import 'package:over_react/src/builder/builder.dart';
 import 'package:path/path.dart' as p;
 import 'package:test/test.dart';
 
 main() {
   group('overReactBuilder', () {
-    final builder = overReactBuilder(null);
-    final logger = Logger('overReactBuilderTestLogger');
-
-    // [1] Note: for this test code to analyze/run in Dart 3 with build_test 3.x,
-    //     it needs to be temporarily modified to use new APIs.
-    //
-    //     We do this in CI, and it can also be done during local development;
-    //     see tool/update_tests_for_dart_3.sh.
-    //
-    //     This is a workaround to us not being able to be compatible with build
-    //     test 2.x and 3.x at the same time, and Dart 2 not being compatible with
-    //     build_test 3.x.
-
-    late AssetReader reader;
-    late InMemoryAssetWriter writer; // [1]
-    late AssetWriterSpy writerSpy;
-    late List<LogRecord> logs;
-
-    setUp(() async {
-      // [1]
-      reader = await PackageAssetReader.currentIsolate(
-        rootPackage: 'over_react',
-      );
+    const testPackagePath = 'test_fixtures/test_packages/builder';
+    late String testPackageName;
+
+    late String outputDirectory;
 
-      writer = InMemoryAssetWriter(); // [1]
-      writerSpy = AssetWriterSpy(writer);
+    setUpAll(() {
+      Process.runSync('dart', ['pub', 'get'], workingDirectory: testPackagePath);
+      testPackageName =
+          RegExp('name: (.+)').firstMatch(File(p.join(testPackagePath, 'pubspec.yaml')).readAsStringSync())!.group(1)!;
+      outputDirectory = Directory.systemTemp.createTempSync().path;
 
-      logs = [];
-      final logSub = logger.onRecord.listen(logs.add);
-      addTearDown(logSub.cancel);
+      // Clean previous build
+      Process.runSync('dart', ['run', 'build_runner', 'clean'], workingDirectory: testPackagePath);
     });
 
-    void verifyNoErrorLogs() {
-      expect(logs.where((log) => log.level >= Level.WARNING), isEmpty,
-        reason: 'Expected no logs at WARNING or SEVERE level, but got:\n'
-          '\t${logs.join('\n\t')}');
+    /// Runs build_runner for a specific file, cleaning first.
+    ProcessResult buildFile(String sourceFilePath) {
+      // Build with filter for the specific file
+      return Process.runSync(
+          'dart',
+          [
+            'run',
+            'build_runner',
+            'build',
+            '--verbose',
+            '--build-filter=lib/${sourceFilePath.replaceAll('.dart', '*.g.dart')}',
+            '--output=$outputDirectory'
+          ],
+          workingDirectory: testPackagePath);
     }
 
-    Future<Null> checkBuildForFile(String assetPath, String expectedOutputAssetPath,
-        String pathToGoldFile) async {
-      final inputAsset = makeAssetId(assetPath);
+    String generatedOutputPath(String sourceFilePath) {
+      return p.join(
+        outputDirectory,
+        'packages',
+        testPackageName,
+        sourceFilePath.replaceAll('.dart', '.over_react.g.dart'),
+      );
+    }
+
+    /// Runs build_runner for a specific file and verifies the generated output matches the gold file.
+    Future<void> checkBuildForFile(String sourceFilePath, String pathToGoldFile) async {
+      final build = buildFile(sourceFilePath);
+
+      expect(build.exitCode, 0,
+          reason: 'build should have succeeded.'
+              '\nstdout: ${build.stdout}'
+              '\nstderr: ${build.stderr}');
+
+      // Read generated file
+      final expectedGeneratedFile = File(generatedOutputPath(sourceFilePath));
+      expect(expectedGeneratedFile.existsSync(), isTrue,
+          reason:
+              'File should have been generated: ${expectedGeneratedFile.path}.\n\nBuild output:\n${build.stdout}\n${build.stderr}');
+
+      // Compare with gold file
       final expectedContent = File(pathToGoldFile).readAsStringSync();
+      final actualContent = expectedGeneratedFile.readAsStringSync();
+
+      expect(actualContent, expectedContent, reason: 'Generated file should match gold file');
+    }
 
-      final expected = {
-        expectedOutputAssetPath : expectedContent
-      };
+    /// Runs build_runner for a specific file and verifies no output is generated.
+    Future<void> checkNoOutputForFile(String sourceFilePath) async {
+      final build = buildFile(sourceFilePath);
 
-      await runBuilder(builder, [inputAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
-      final actual = writerSpy.assetsWritten;
+      expect(build.exitCode, 0,
+          reason: 'build should have succeeded.'
+              '\nstdout: ${build.stdout}'
+              '\nstderr: ${build.stderr}');
 
-      checkOutputs(expected, actual, writer);
-      verifyNoErrorLogs();
+      // Verify no generated file exists
+      final expectedGeneratedFile = File(generatedOutputPath(sourceFilePath));
+      expect(expectedGeneratedFile.existsSync(), isFalse,
+          reason: 'File should not have been generated: ${expectedGeneratedFile.path}');
     }
 
-    test('does not produce a build output for a file with no over_react annotations', () async {
-      var basicAsset = makeAssetId('over_react|test_fixtures/source_files/no_annotations.dart');
-      await runBuilder(builder, [basicAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
+    /// Runs build_runner for a specific file and verifies a warning appears in the output.
+    Future<void> checkWarningForFile(String sourceFilePath, String expectedWarning) async {
+      final build = buildFile(sourceFilePath);
+
+      // Check for expected warning in output
+      expect('${build.stdout}${build.stderr}', contains(expectedWarning),
+          reason: 'Expected warning not found in build output');
+
+      expect(build.exitCode, 0,
+          reason: 'build should have succeeded.'
+              '\nstdout: ${build.stdout}'
+              '\nstderr: ${build.stderr}');
+    }
+
+    /// Runs build_runner for a specific file and verifies a severe error appears in the output.
+    Future<void> checkSevereErrorForFile(String sourceFilePath, String expectedError) async {
+      final build = buildFile(sourceFilePath);
 
-      expect(writerSpy.assetsWritten, isEmpty);
-      verifyNoErrorLogs();
+      // Check for expected error in output
+      expect('${build.stdout}${build.stderr}', contains(expectedError),
+          reason: 'Expected error not found in build output');
+
+      expect(build.exitCode, 1,
+          reason: 'build should have failed.'
+              '\nstdout: ${build.stdout}'
+              '\nstderr: ${build.stderr}');
+    }
+
+    test('does not produce a build output for a file with no over_react annotations', () async {
+      await checkNoOutputForFile('no_annotations.dart');
     });
 
-    test('warns if .over_react.g.dart part directive is present and no declarations are present, but no code is generated', () async {
-      var libraryAsset = makeAssetId('over_react|test_fixtures/source_files/has_part_directive_missing_gen/no_declarations.dart');
-      await runBuilder(builder, [libraryAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
-      final expectedWarning = logs.firstWhereOrNull((log) {
-        return log.level == Level.WARNING && log.message == 'An over_react part directive was found in test_fixtures/source_files/has_part_directive_missing_gen/no_declarations.dart, but no code was generated. The part directive may be unnecessary if the file does not contain any concrete components or abstract state/props classes.';
-      });
-      expect(expectedWarning, isNotNull,
-        reason: 'Expected a WARNING log for a part directive being present in a file with no generated output.');
+    test(
+        'warns if .over_react.g.dart part directive is present and no declarations are present, but no code is generated',
+        () async {
+      await checkWarningForFile('has_part_directive_missing_gen/no_declarations.dart',
+          'An over_react part directive was found in lib/has_part_directive_missing_gen/no_declarations.dart, but no code was generated.');
     });
 
-    test('warns if .over_react.g.dart part directive is present and declarations are present, but no code is generated', () async {
-      var libraryAsset = makeAssetId('over_react|test_fixtures/source_files/has_part_directive_missing_gen/with_declarations.dart');
-      await runBuilder(builder, [libraryAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
-      final expectedWarning = logs.firstWhereOrNull((log) {
-        return log.level == Level.WARNING && log.message == 'An over_react part directive was found in test_fixtures/source_files/has_part_directive_missing_gen/with_declarations.dart, but no code was generated. The part directive may be unnecessary if the file does not contain any concrete components or abstract state/props classes.';
-      });
-      expect(expectedWarning, isNotNull,
-        reason: 'Expected a WARNING log for a part directive being present in a file with no generated output.');
+    test('warns if .over_react.g.dart part directive is present and declarations are present, but no code is generated',
+        () async {
+      await checkWarningForFile('has_part_directive_missing_gen/with_declarations.dart',
+          'An over_react part directive was found in lib/has_part_directive_missing_gen/with_declarations.dart, but no code was generated.');
     });
 
     group('for backwards compatible boilerplate:', () {
       test('builds from basic component file', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/backwards_compatible/basic.dart',
-            'over_react|test_fixtures/source_files/backwards_compatible/basic.over_react.g.dart',
+        await checkBuildForFile('backwards_compatible/basic.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/backwards_compatible/basic.over_react.g.dart.goldFile');
       });
 
       test('builds from basic multi-part library', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/backwards_compatible/basic_library.dart',
-            'over_react|test_fixtures/source_files/backwards_compatible/basic_library.over_react.g.dart',
+        await checkBuildForFile('backwards_compatible/basic_library.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/backwards_compatible/basic_library.over_react.g.dart.goldFile');
       });
 
       test('builds for props mixins', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/backwards_compatible/props_mixin.dart',
-            'over_react|test_fixtures/source_files/backwards_compatible/props_mixin.over_react.g.dart',
+        await checkBuildForFile('backwards_compatible/props_mixin.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/backwards_compatible/props_mixin.over_react.g.dart.goldFile');
       });
 
       test('builds for state mixins', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/backwards_compatible/state_mixin.dart',
-            'over_react|test_fixtures/source_files/backwards_compatible/state_mixin.over_react.g.dart',
+        await checkBuildForFile('backwards_compatible/state_mixin.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/backwards_compatible/state_mixin.over_react.g.dart.goldFile');
       });
 
       test('does not produce a build output for just a part file', () async {
-        var basicAsset = makeAssetId('over_react|test_fixtures/source_files/backwards_compatible/part_of_basic_library.dart');
-        await runBuilder(builder, [basicAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
-
-        expect(writerSpy.assetsWritten, isEmpty);
-        verifyNoErrorLogs();
+        await checkNoOutputForFile('backwards_compatible/part_of_basic_library.dart');
       });
     });
 
     group('for Dart 2 only compatible boilerplate:', () {
       test('builds from basic component file', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/dart2_only/basic.dart',
-            'over_react|test_fixtures/source_files/dart2_only/basic.over_react.g.dart',
+        await checkBuildForFile('dart2_only/basic.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/basic.over_react.g.dart.goldFile');
       });
 
       test('builds from basic multi-part library', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/dart2_only/basic_library.dart',
-            'over_react|test_fixtures/source_files/dart2_only/basic_library.over_react.g.dart',
+        await checkBuildForFile('dart2_only/basic_library.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/basic_library.over_react.g.dart.goldFile');
       });
 
       test('builds for props mixins', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/dart2_only/props_mixin.dart',
-            'over_react|test_fixtures/source_files/dart2_only/props_mixin.over_react.g.dart',
+        await checkBuildForFile('dart2_only/props_mixin.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/props_mixin.over_react.g.dart.goldFile');
       });
 
       test('builds for state mixins', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/dart2_only/state_mixin.dart',
-            'over_react|test_fixtures/source_files/dart2_only/state_mixin.over_react.g.dart',
+        await checkBuildForFile('dart2_only/state_mixin.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/state_mixin.over_react.g.dart.goldFile');
       });
 
       test('does not produce a build output for just a part file', () async {
-        var basicAsset = makeAssetId('over_react|test_fixtures/source_files/dart2_only/part_of_basic_library.dart');
-        await runBuilder(builder, [basicAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
-
-        expect(writerSpy.assetsWritten, isEmpty);
-        verifyNoErrorLogs();
+        await checkNoOutputForFile('dart2_only/part_of_basic_library.dart');
       });
 
       test('fails if the .over_react.g.dart part directive is missing', () async {
-        var libraryAsset = makeAssetId('over_react|test_fixtures/source_files/dart2_only/missing_over_react_g_part/library.dart');
-        await runBuilder(builder, [libraryAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
-        final expectedLog = logs.firstWhereOrNull((log) {
-          return log.level == Level.SEVERE && log.message == 'Missing "part \'library.over_react.g.dart\';".';
-        });
-        expect(expectedLog, isNotNull,
-            reason: 'Expected a SEVERE log for the missing over_react part.');
+        await checkSevereErrorForFile(
+            'dart2_only/missing_over_react_g_part/library.dart', 'Missing "part \'library.over_react.g.dart\';".');
       });
 
       group('for Component2:', () {
         test('builds from basic component file', () async {
-          await checkBuildForFile(
-              'over_react|test_fixtures/source_files/dart2_only/component2/basic.dart',
-              'over_react|test_fixtures/source_files/dart2_only/component2/basic.over_react.g.dart',
+          await checkBuildForFile('dart2_only/component2/basic.dart',
               '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/component2/basic.over_react.g.dart.goldFile');
         });
 
         test('builds from basic multi-part library', () async {
-          await checkBuildForFile(
-              'over_react|test_fixtures/source_files/dart2_only/component2/basic_library.dart',
-              'over_react|test_fixtures/source_files/dart2_only/component2/basic_library.over_react.g.dart',
+          await checkBuildForFile('dart2_only/component2/basic_library.dart',
               '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/component2/basic_library.over_react.g.dart.goldFile');
         });
       });
@@ -213,63 +213,42 @@ main() {
 
     group('for mixin based boilerplate:', () {
       test('builds from basic component file', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/mixin_based/basic.dart',
-            'over_react|test_fixtures/source_files/mixin_based/basic.over_react.g.dart',
+        await checkBuildForFile('mixin_based/basic.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/mixin_based/basic.over_react.g.dart.goldFile');
       });
 
       test('builds from basic component file using Dart >=2.9.0 syntax', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/mixin_based/basic_two_nine.dart',
-            'over_react|test_fixtures/source_files/mixin_based/basic_two_nine.over_react.g.dart',
+        await checkBuildForFile('mixin_based/basic_two_nine.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/mixin_based/basic_two_nine.over_react.g.dart.goldFile');
       });
 
       test('builds from basic multi-part library', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/mixin_based/basic_library.dart',
-            'over_react|test_fixtures/source_files/mixin_based/basic_library.over_react.g.dart',
+        await checkBuildForFile('mixin_based/basic_library.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/mixin_based/basic_library.over_react.g.dart.goldFile');
       });
 
       test('builds when props mixins and classes have type parameters', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/mixin_based/type_parameters.dart',
-            'over_react|test_fixtures/source_files/mixin_based/type_parameters.over_react.g.dart',
+        await checkBuildForFile('mixin_based/type_parameters.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/mixin_based/type_parameters.over_react.g.dart.goldFile');
       });
 
       test('builds for props mixins', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/mixin_based/props_mixin.dart',
-            'over_react|test_fixtures/source_files/mixin_based/props_mixin.over_react.g.dart',
+        await checkBuildForFile('mixin_based/props_mixin.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/mixin_based/props_mixin.over_react.g.dart.goldFile');
       });
 
       test('builds for state mixins', () async {
-        await checkBuildForFile(
-            'over_react|test_fixtures/source_files/mixin_based/state_mixin.dart',
-            'over_react|test_fixtures/source_files/mixin_based/state_mixin.over_react.g.dart',
+        await checkBuildForFile('mixin_based/state_mixin.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/mixin_based/state_mixin.over_react.g.dart.goldFile');
       });
 
       test('does not produce a build output for just a part file', () async {
-        var basicAsset = makeAssetId('over_react|test_fixtures/source_files/mixin_based/part_of_basic_library.dart');
-        await runBuilder(builder, [basicAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
-
-        expect(writerSpy.assetsWritten, isEmpty);
-        verifyNoErrorLogs();
+        await checkNoOutputForFile('mixin_based/part_of_basic_library.dart');
       });
 
       test('fails if the .over_react.g.dart part directive is missing', () async {
-        var libraryAsset = makeAssetId('over_react|test_fixtures/source_files/mixin_based/missing_over_react_g_part/library.dart');
-        await runBuilder(builder, [libraryAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
-        final expectedLog = logs.firstWhereOrNull((log) {
-          return log.level == Level.SEVERE && log.message == 'Missing "part \'library.over_react.g.dart\';".';
-        });
-        expect(expectedLog, isNotNull,
-            reason: 'Expected a SEVERE log for the missing over_react part.');
+        await checkSevereErrorForFile(
+            'mixin_based/missing_over_react_g_part/library.dart', 'Missing "part \'library.over_react.g.dart\';".');
       });
     });
   });
diff --git a/test_fixtures/gold_output_files/README.md b/test_fixtures/gold_output_files/README.md
index d44e8a763..51ce5a883 100644
--- a/test_fixtures/gold_output_files/README.md
+++ b/test_fixtures/gold_output_files/README.md
@@ -4,8 +4,3 @@ To re-generate the gold files in this directory using the over_react builder, ru
 ```sh
 dart tool/update_gold_output_files.dart
 ```
-
-If that deletes other generated files throughout over_react (which usually only happens after it prompts you about conflicting outputs), you can restore them by running a build: 
-```sh
-dart run build_runner build
-```
diff --git a/test_fixtures/gold_output_files/backwards_compatible/basic.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/backwards_compatible/basic.over_react.g.dart.goldFile
index c9dad6aeb..55e7ae951 100644
--- a/test_fixtures/gold_output_files/backwards_compatible/basic.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/backwards_compatible/basic.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'basic.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/backwards_compatible/basic_library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/backwards_compatible/basic_library.over_react.g.dart.goldFile
index 0604d488c..a9e9ba62a 100644
--- a/test_fixtures/gold_output_files/backwards_compatible/basic_library.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/backwards_compatible/basic_library.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'basic_library.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/backwards_compatible/props_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/backwards_compatible/props_mixin.over_react.g.dart.goldFile
index fb38d2d70..ebc38bc05 100644
--- a/test_fixtures/gold_output_files/backwards_compatible/props_mixin.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/backwards_compatible/props_mixin.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'props_mixin.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 mixin $ExamplePropsMixinClass implements ExamplePropsMixinClass {
diff --git a/test_fixtures/gold_output_files/backwards_compatible/state_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/backwards_compatible/state_mixin.over_react.g.dart.goldFile
index 50441b831..694b687b8 100644
--- a/test_fixtures/gold_output_files/backwards_compatible/state_mixin.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/backwards_compatible/state_mixin.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'state_mixin.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 mixin $ExampleStateMixinClass implements ExampleStateMixinClass {
diff --git a/test_fixtures/gold_output_files/dart2_only/basic.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/basic.over_react.g.dart.goldFile
index 23cc8811c..e0ffcf49d 100644
--- a/test_fixtures/gold_output_files/dart2_only/basic.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/dart2_only/basic.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'basic.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/dart2_only/basic_library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/basic_library.over_react.g.dart.goldFile
index 1241e104c..7091f3ed6 100644
--- a/test_fixtures/gold_output_files/dart2_only/basic_library.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/dart2_only/basic_library.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'basic_library.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/dart2_only/component2/basic.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/component2/basic.over_react.g.dart.goldFile
index 33eacf32d..bc240ca45 100644
--- a/test_fixtures/gold_output_files/dart2_only/component2/basic.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/dart2_only/component2/basic.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'basic.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/dart2_only/component2/basic_library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/component2/basic_library.over_react.g.dart.goldFile
index 133328db7..9d85fb827 100644
--- a/test_fixtures/gold_output_files/dart2_only/component2/basic_library.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/dart2_only/component2/basic_library.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'basic_library.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/dart2_only/missing_over_react_g_part/library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/missing_over_react_g_part/library.over_react.g.dart.goldFile
index c5a5cfaab..80b499df2 100644
--- a/test_fixtures/gold_output_files/dart2_only/missing_over_react_g_part/library.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/dart2_only/missing_over_react_g_part/library.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'library.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/dart2_only/props_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/props_mixin.over_react.g.dart.goldFile
index fcbc1480f..699e1b137 100644
--- a/test_fixtures/gold_output_files/dart2_only/props_mixin.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/dart2_only/props_mixin.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'props_mixin.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 @deprecated
diff --git a/test_fixtures/gold_output_files/dart2_only/state_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/state_mixin.over_react.g.dart.goldFile
index 9b9ae55ba..654217512 100644
--- a/test_fixtures/gold_output_files/dart2_only/state_mixin.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/dart2_only/state_mixin.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'state_mixin.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 @deprecated
diff --git a/test_fixtures/gold_output_files/mixin_based/basic.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/mixin_based/basic.over_react.g.dart.goldFile
index 60832ea4d..c3bb17214 100644
--- a/test_fixtures/gold_output_files/mixin_based/basic.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/mixin_based/basic.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'basic.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/mixin_based/basic_library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/mixin_based/basic_library.over_react.g.dart.goldFile
index ee8e5dbb1..0f2a0c1d5 100644
--- a/test_fixtures/gold_output_files/mixin_based/basic_library.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/mixin_based/basic_library.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'basic_library.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/mixin_based/basic_two_nine.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/mixin_based/basic_two_nine.over_react.g.dart.goldFile
index 7d886e85d..e2544b8c6 100644
--- a/test_fixtures/gold_output_files/mixin_based/basic_two_nine.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/mixin_based/basic_two_nine.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'basic_two_nine.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/mixin_based/missing_over_react_g_part/library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/mixin_based/missing_over_react_g_part/library.over_react.g.dart.goldFile
index c5a17450f..427f3bb1d 100644
--- a/test_fixtures/gold_output_files/mixin_based/missing_over_react_g_part/library.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/mixin_based/missing_over_react_g_part/library.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'library.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/mixin_based/props_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/mixin_based/props_mixin.over_react.g.dart.goldFile
index ebfd5ee4f..227063fcd 100644
--- a/test_fixtures/gold_output_files/mixin_based/props_mixin.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/mixin_based/props_mixin.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'props_mixin.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 @Deprecated('This API is for use only within generated code.'
diff --git a/test_fixtures/gold_output_files/mixin_based/state_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/mixin_based/state_mixin.over_react.g.dart.goldFile
index 205f3a9b7..9adca711a 100644
--- a/test_fixtures/gold_output_files/mixin_based/state_mixin.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/mixin_based/state_mixin.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'state_mixin.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 @Deprecated('This API is for use only within generated code.'
diff --git a/test_fixtures/gold_output_files/mixin_based/two_nine_with_multiple_factories.over_react.g.dart.goldfile b/test_fixtures/gold_output_files/mixin_based/two_nine_with_multiple_factories.over_react.g.dart.goldfile
index 2a7de8bf5..7998b508f 100644
--- a/test_fixtures/gold_output_files/mixin_based/two_nine_with_multiple_factories.over_react.g.dart.goldfile
+++ b/test_fixtures/gold_output_files/mixin_based/two_nine_with_multiple_factories.over_react.g.dart.goldfile
@@ -6,6 +6,8 @@ part of 'two_nine_with_multiple_factories.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 // React component factory implementation.
diff --git a/test_fixtures/gold_output_files/mixin_based/type_parameters.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/mixin_based/type_parameters.over_react.g.dart.goldFile
index 54b22a581..07ffd9eba 100644
--- a/test_fixtures/gold_output_files/mixin_based/type_parameters.over_react.g.dart.goldFile
+++ b/test_fixtures/gold_output_files/mixin_based/type_parameters.over_react.g.dart.goldFile
@@ -6,6 +6,8 @@ part of 'type_parameters.dart';
 
 // **************************************************************************
 // OverReactBuilder (package:over_react/src/builder.dart)
+//
+// Using nullSafety: false. {languageVersion: 2.11, source: libraryVersionComment}
 // **************************************************************************
 
 @Deprecated('This API is for use only within generated code.'
diff --git a/test_fixtures/test_packages/builder/analysis_options.yaml b/test_fixtures/test_packages/builder/analysis_options.yaml
new file mode 100644
index 000000000..e69de29bb
diff --git a/test_fixtures/source_files/backwards_compatible/basic.dart b/test_fixtures/test_packages/builder/lib/backwards_compatible/basic.dart
similarity index 100%
rename from test_fixtures/source_files/backwards_compatible/basic.dart
rename to test_fixtures/test_packages/builder/lib/backwards_compatible/basic.dart
diff --git a/test_fixtures/source_files/backwards_compatible/basic_library.dart b/test_fixtures/test_packages/builder/lib/backwards_compatible/basic_library.dart
similarity index 100%
rename from test_fixtures/source_files/backwards_compatible/basic_library.dart
rename to test_fixtures/test_packages/builder/lib/backwards_compatible/basic_library.dart
diff --git a/test_fixtures/source_files/backwards_compatible/part_of_basic_library.dart b/test_fixtures/test_packages/builder/lib/backwards_compatible/part_of_basic_library.dart
similarity index 100%
rename from test_fixtures/source_files/backwards_compatible/part_of_basic_library.dart
rename to test_fixtures/test_packages/builder/lib/backwards_compatible/part_of_basic_library.dart
diff --git a/test_fixtures/source_files/backwards_compatible/part_of_basic_library_2.dart b/test_fixtures/test_packages/builder/lib/backwards_compatible/part_of_basic_library_2.dart
similarity index 100%
rename from test_fixtures/source_files/backwards_compatible/part_of_basic_library_2.dart
rename to test_fixtures/test_packages/builder/lib/backwards_compatible/part_of_basic_library_2.dart
diff --git a/test_fixtures/source_files/backwards_compatible/props_mixin.dart b/test_fixtures/test_packages/builder/lib/backwards_compatible/props_mixin.dart
similarity index 100%
rename from test_fixtures/source_files/backwards_compatible/props_mixin.dart
rename to test_fixtures/test_packages/builder/lib/backwards_compatible/props_mixin.dart
diff --git a/test_fixtures/source_files/backwards_compatible/state_mixin.dart b/test_fixtures/test_packages/builder/lib/backwards_compatible/state_mixin.dart
similarity index 100%
rename from test_fixtures/source_files/backwards_compatible/state_mixin.dart
rename to test_fixtures/test_packages/builder/lib/backwards_compatible/state_mixin.dart
diff --git a/test_fixtures/source_files/dart2_only/basic.dart b/test_fixtures/test_packages/builder/lib/dart2_only/basic.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/basic.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/basic.dart
diff --git a/test_fixtures/source_files/dart2_only/basic_library.dart b/test_fixtures/test_packages/builder/lib/dart2_only/basic_library.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/basic_library.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/basic_library.dart
diff --git a/test_fixtures/source_files/dart2_only/component2/basic.dart b/test_fixtures/test_packages/builder/lib/dart2_only/component2/basic.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/component2/basic.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/component2/basic.dart
diff --git a/test_fixtures/source_files/dart2_only/component2/basic_library.dart b/test_fixtures/test_packages/builder/lib/dart2_only/component2/basic_library.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/component2/basic_library.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/component2/basic_library.dart
diff --git a/test_fixtures/source_files/dart2_only/component2/part_of_basic_library.dart b/test_fixtures/test_packages/builder/lib/dart2_only/component2/part_of_basic_library.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/component2/part_of_basic_library.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/component2/part_of_basic_library.dart
diff --git a/test_fixtures/source_files/dart2_only/component2/part_of_basic_library_2.dart b/test_fixtures/test_packages/builder/lib/dart2_only/component2/part_of_basic_library_2.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/component2/part_of_basic_library_2.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/component2/part_of_basic_library_2.dart
diff --git a/test_fixtures/source_files/dart2_only/missing_over_react_g_part/library.dart b/test_fixtures/test_packages/builder/lib/dart2_only/missing_over_react_g_part/library.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/missing_over_react_g_part/library.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/missing_over_react_g_part/library.dart
diff --git a/test_fixtures/source_files/dart2_only/missing_over_react_g_part/part.dart b/test_fixtures/test_packages/builder/lib/dart2_only/missing_over_react_g_part/part.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/missing_over_react_g_part/part.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/missing_over_react_g_part/part.dart
diff --git a/test_fixtures/source_files/dart2_only/part_of_basic_library.dart b/test_fixtures/test_packages/builder/lib/dart2_only/part_of_basic_library.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/part_of_basic_library.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/part_of_basic_library.dart
diff --git a/test_fixtures/source_files/dart2_only/part_of_basic_library.g.dart b/test_fixtures/test_packages/builder/lib/dart2_only/part_of_basic_library.g.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/part_of_basic_library.g.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/part_of_basic_library.g.dart
diff --git a/test_fixtures/source_files/dart2_only/part_of_basic_library_2.dart b/test_fixtures/test_packages/builder/lib/dart2_only/part_of_basic_library_2.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/part_of_basic_library_2.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/part_of_basic_library_2.dart
diff --git a/test_fixtures/source_files/dart2_only/props_mixin.dart b/test_fixtures/test_packages/builder/lib/dart2_only/props_mixin.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/props_mixin.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/props_mixin.dart
diff --git a/test_fixtures/source_files/dart2_only/state_mixin.dart b/test_fixtures/test_packages/builder/lib/dart2_only/state_mixin.dart
similarity index 100%
rename from test_fixtures/source_files/dart2_only/state_mixin.dart
rename to test_fixtures/test_packages/builder/lib/dart2_only/state_mixin.dart
diff --git a/test_fixtures/source_files/has_part_directive_missing_gen/no_declarations.dart b/test_fixtures/test_packages/builder/lib/has_part_directive_missing_gen/no_declarations.dart
similarity index 100%
rename from test_fixtures/source_files/has_part_directive_missing_gen/no_declarations.dart
rename to test_fixtures/test_packages/builder/lib/has_part_directive_missing_gen/no_declarations.dart
diff --git a/test_fixtures/source_files/has_part_directive_missing_gen/with_declarations.dart b/test_fixtures/test_packages/builder/lib/has_part_directive_missing_gen/with_declarations.dart
similarity index 100%
rename from test_fixtures/source_files/has_part_directive_missing_gen/with_declarations.dart
rename to test_fixtures/test_packages/builder/lib/has_part_directive_missing_gen/with_declarations.dart
diff --git a/test_fixtures/source_files/mixin_based/basic.dart b/test_fixtures/test_packages/builder/lib/mixin_based/basic.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/basic.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/basic.dart
diff --git a/test_fixtures/source_files/mixin_based/basic_library.dart b/test_fixtures/test_packages/builder/lib/mixin_based/basic_library.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/basic_library.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/basic_library.dart
diff --git a/test_fixtures/source_files/mixin_based/basic_two_nine.dart b/test_fixtures/test_packages/builder/lib/mixin_based/basic_two_nine.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/basic_two_nine.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/basic_two_nine.dart
diff --git a/test_fixtures/source_files/mixin_based/missing_over_react_g_part/library.dart b/test_fixtures/test_packages/builder/lib/mixin_based/missing_over_react_g_part/library.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/missing_over_react_g_part/library.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/missing_over_react_g_part/library.dart
diff --git a/test_fixtures/source_files/mixin_based/missing_over_react_g_part/part.dart b/test_fixtures/test_packages/builder/lib/mixin_based/missing_over_react_g_part/part.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/missing_over_react_g_part/part.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/missing_over_react_g_part/part.dart
diff --git a/test_fixtures/source_files/mixin_based/part_of_basic_library.dart b/test_fixtures/test_packages/builder/lib/mixin_based/part_of_basic_library.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/part_of_basic_library.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/part_of_basic_library.dart
diff --git a/test_fixtures/source_files/mixin_based/part_of_basic_library_2.dart b/test_fixtures/test_packages/builder/lib/mixin_based/part_of_basic_library_2.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/part_of_basic_library_2.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/part_of_basic_library_2.dart
diff --git a/test_fixtures/source_files/mixin_based/props_mixin.dart b/test_fixtures/test_packages/builder/lib/mixin_based/props_mixin.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/props_mixin.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/props_mixin.dart
diff --git a/test_fixtures/source_files/mixin_based/state_mixin.dart b/test_fixtures/test_packages/builder/lib/mixin_based/state_mixin.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/state_mixin.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/state_mixin.dart
diff --git a/test_fixtures/source_files/mixin_based/two_nine_with_multiple_factories.dart b/test_fixtures/test_packages/builder/lib/mixin_based/two_nine_with_multiple_factories.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/two_nine_with_multiple_factories.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/two_nine_with_multiple_factories.dart
diff --git a/test_fixtures/source_files/mixin_based/type_parameters.dart b/test_fixtures/test_packages/builder/lib/mixin_based/type_parameters.dart
similarity index 100%
rename from test_fixtures/source_files/mixin_based/type_parameters.dart
rename to test_fixtures/test_packages/builder/lib/mixin_based/type_parameters.dart
diff --git a/test_fixtures/source_files/no_annotations.dart b/test_fixtures/test_packages/builder/lib/no_annotations.dart
similarity index 100%
rename from test_fixtures/source_files/no_annotations.dart
rename to test_fixtures/test_packages/builder/lib/no_annotations.dart
diff --git a/test_fixtures/test_packages/builder/pubspec.yaml b/test_fixtures/test_packages/builder/pubspec.yaml
new file mode 100644
index 000000000..1e9867114
--- /dev/null
+++ b/test_fixtures/test_packages/builder/pubspec.yaml
@@ -0,0 +1,9 @@
+name: over_react__test__builder_tests
+publish_to: none
+environment:
+  sdk: ">=2.19.0 <4.0.0"
+dependencies:
+  over_react:
+    path: ../../../
+dev_dependencies:
+  build_runner: any
diff --git a/tool/update_gold_output_files.dart b/tool/update_gold_output_files.dart
index 1e15b4d07..7386f278e 100644
--- a/tool/update_gold_output_files.dart
+++ b/tool/update_gold_output_files.dart
@@ -3,56 +3,43 @@ import 'dart:io';
 import 'package:glob/glob.dart';
 import 'package:glob/list_local_fs.dart';
 import 'package:path/path.dart' as p;
+import 'package:yaml/yaml.dart';
 
-final sourceFixturesDir = Directory('test_fixtures/source_files');
+final sourceFixtureDir = Directory('test_fixtures/test_packages/builder');
 final goldsDir = Directory('test_fixtures/gold_output_files');
 
-/// A temporary directory used to generate new golds.
-final tmpSourceDir = Directory('test/tmp_test_files');
-
-/// Updates gold files in [goldsDir] by re-generating them from a copy of the files in [sourceFixturesDir].
+/// Updates gold files in [goldsDir] by re-generating them from a copy of the files in [sourceFixtureDir].
 Future<void> main() async {
-  print('Copying files from ${sourceFixturesDir.path} to temporary directory ${tmpSourceDir.path}');
-  if (tmpSourceDir.existsSync()) tmpSourceDir.deleteSync(recursive: true);
-  tmpSourceDir.createSync(recursive: true);
-  for (final file in Glob(p.join(sourceFixturesDir.path, '**')).listSync().whereType<File>()) {
-    final newPath = p.join(tmpSourceDir.path, p.relative(file.path, from: sourceFixturesDir.path));
-    File(newPath).parent.createSync(recursive: true);
-    file.copySync(newPath);
-  }
+  final sourceFixturePubspec =
+      loadYaml(File(p.join(sourceFixtureDir.path, 'pubspec.yaml')).readAsStringSync());
+  final sourceFixturePackageName = sourceFixturePubspec['name'] as String;
 
-  print('Building files in temporary directory ${tmpSourceDir.path}');
-  final buildProcess = await Process.start(
-      'dart', ['run', 'build_runner', 'build', '--build-filter=${p.join(tmpSourceDir.path, '**')}'],
-      mode: ProcessStartMode.inheritStdio);
+  print('Building files in test fixture ${goldsDir.path}');
+
+  print('Building files in ${sourceFixtureDir.path} to .dart_tool...');
+  final buildProcess = await Process.start('dart', ['run', 'build_runner', 'build'],
+      workingDirectory: sourceFixtureDir.path, mode: ProcessStartMode.inheritStdio);
   // Wait for build to complete.
   final buildExitCode = await buildProcess.exitCode;
   if (buildExitCode != 0) {
     stderr.writeln(
-        '^ Build failures are expected for "missing_over_react_g_part" files, and can be ignored.');
+        '\n^ Build failures are expected for "missing_over_react_g_part" files, and can be ignored.\n');
   }
 
   print('Copying built files to golds directory ${goldsDir.path}');
-  final generatedTmpFiles =
-      Glob(p.join(tmpSourceDir.path, '**.over_react.g.dart')).listSync().whereType<File>().toList();
-  if (generatedTmpFiles.isEmpty) {
-    throw Exception('No generated files were found in ${tmpSourceDir.path}.'
-        ' Ensure in build.yaml the over_react builder runs on directory with build_to:source');
+  final outputPath = p.join(
+      sourceFixtureDir.path, '.dart_tool', 'build', 'generated', sourceFixturePackageName, 'lib');
+  late final generatedTmpFiles =
+      Glob(p.join(outputPath, '**.over_react.g.dart')).listSync().whereType<File>().toList();
+  if (!Directory(outputPath).existsSync() || generatedTmpFiles.isEmpty) {
+    throw Exception(
+        'No generated files were found in $outputPath; something is probably wrong with the paths in this script.');
   }
   for (final file in generatedTmpFiles) {
-    final newPath =
-        p.join(goldsDir.path, p.relative(file.path, from: tmpSourceDir.path)) + '.goldFile';
+    final newPath = p.join(goldsDir.path, p.relative(file.path, from: outputPath)) + '.goldFile';
     File(newPath).parent.createSync(recursive: true);
     file.copySync(newPath);
   }
 
-  print('Cleaning up temporary directory ${tmpSourceDir.path}');
-  tmpSourceDir.deleteSync(recursive: true);
-
   print('Done!');
-
-  print('\nIf non-gold generated files throughout this package got deleted'
-      ' (which usually only happens after it prompts you about conflicting outputs),'
-      ' you can restore them by running a build:\n\n'
-      '    dart run build_runner build');
 }
diff --git a/tool/update_tests_for_dart_3.sh b/tool/update_tests_for_dart_3.sh
deleted file mode 100755
index c1c8b06a3..000000000
--- a/tool/update_tests_for_dart_3.sh
+++ /dev/null
@@ -1,18 +0,0 @@
-#!/usr/bin/env bash
-
-#
-# This script makes updates to tests to make them compatible with Dart 3.
-# This is a last-resort workaround for cases that can't analyze cleanly in both versions.
-#
-
-set -e
-set -x
-
-# Update over_react_builder_test.dart by applying a patch in build_test 3 (Dart 3 only);
-# see comment in test file for more details on the changes.
-build_test_version=$(yq '.packages.build_test.version' pubspec.lock)
-if [[ "$build_test_version" == "3."* ]]; then
-  # This patch is derived from fixing tests in build_test 3 and getting the diff with:
-  #    git diff test/vm_tests/builder/over_react_builder_test.dart > tool/update_tests_for_dart_3/build_test_3_updates.patch
-  git apply tool/update_tests_for_dart_3/build_test_3_updates.patch
-fi
diff --git a/tool/update_tests_for_dart_3/build_test_3_updates.patch b/tool/update_tests_for_dart_3/build_test_3_updates.patch
deleted file mode 100644
index 616526fbc..000000000
--- a/tool/update_tests_for_dart_3/build_test_3_updates.patch
+++ /dev/null
@@ -1,45 +0,0 @@
-diff --git a/test/vm_tests/builder/over_react_builder_test.dart b/test/vm_tests/builder/over_react_builder_test.dart
-index 48c96b62..b9b60b55 100644
---- a/test/vm_tests/builder/over_react_builder_test.dart
-+++ b/test/vm_tests/builder/over_react_builder_test.dart
-@@ -20,6 +20,8 @@ import 'package:build/build.dart';
- import 'package:build_resolvers/build_resolvers.dart';
- import 'package:build_test/build_test.dart';
- import 'package:collection/collection.dart' show IterableExtension;
-+import 'package:glob/glob.dart';
-+import 'package:glob/list_local_fs.dart';
- import 'package:logging/logging.dart';
- import 'package:over_react/src/builder/builder.dart';
- import 'package:path/path.dart' as p;
-@@ -40,18 +42,27 @@ main() {
-     //     test 2.x and 3.x at the same time, and Dart 2 not being compatible with
-     //     build_test 3.x.
-
--    late AssetReader reader;
--    late InMemoryAssetWriter writer; // [1]
-+    late TestReaderWriter reader;
-+    late TestReaderWriter writer; // [1]
-     late AssetWriterSpy writerSpy;
-     late List<LogRecord> logs;
-
-     setUp(() async {
-       // [1]
--      reader = await PackageAssetReader.currentIsolate(
-+      reader = TestReaderWriter(
-         rootPackage: 'over_react',
-       );
-
--      writer = InMemoryAssetWriter(); // [1]
-+      // Load test fixture assets from the filesystem into the test reader.
-+      for (final file in Glob('test_fixtures/**').listSync().whereType<File>()) {
-+        // Write via `testing` so it's not tracked as a builder output.
-+        reader.testing.writeBytes(
-+          makeAssetId('over_react|${file.path}'),
-+          file.readAsBytesSync(),
-+        );
-+      }
-+
-+      writer = TestReaderWriter(); // [1]
-       writerSpy = AssetWriterSpy(writer);
-
-       logs = [];