anchor.diff:  main() {
     defineReflectiveSuite(() {
       defineReflectiveTests(_InstrumentationTest);
  +    defineReflectiveTests(_InstrumentationTestWithFixBuilder);
     });
   }
   
   class _InstrumentationClient implements NullabilityMigrationInstrumentation {
  -  final _InstrumentationTest test;
  +  final _InstrumentationTestBase test;
   
     _InstrumentationClient(this.test);
   
  
positive.code:   FindNode findNode;
  
    Source source;
  
    Future<void> analyze(String content) async {
      var sourcePath = convertPath('/home/test/lib/test.dart');
      newFile(sourcePath, content: content);
      var listener = new TestMigrationListener();
      var migration = NullabilityMigration(listener,
          instrumentation: _InstrumentationClient(this));
      var result = await session.getResolvedUnit(sourcePath);
      source = result.unit.declaredElement.source;
      findNode = FindNode(content, result.unit);
  
negative.code:         (e) => e.sourceNode == node && e.destinationNode == never && e.isHard);
    }
  }
  
  @reflectiveTest
  class _InstrumentationTestWithFixBuilder extends _InstrumentationTestBase {
    @override
    bool get useFixBuilder => true;
  
    @override
    @FailingTest(issue: 'https://github.com/dart-lang/sdk/issues/38472')
    Future<void> test_fix_reason_edge() => super.test_fix_reason_edge();
  
    @override
    @FailingTest(issue: 'https://github.com/dart-lang/sdk/issues/38472')
    Future<void> test_fix_reason_node() => super.test_fix_reason_node();
  }
  