anchor.diff:    }
   
     test_mixin_inference_nullSafety2() async {
  -    featureSet = enableNnbd;
  +    featureSet = featureSetNullSafe;
       addLibrarySource('/a.dart', r'''
   class A<T> {}
   
  
positive.code:   }
  
    test_inferred_type_nullability_class_ref_question() async {
      featureSet = enableNnbd;
      addSource('/a.dart', 'int? f() => 0;');
      var library = await checkLibrary('''
  import 'a.dart';
  
negative.code: /// applied to a class implementing [ResynthesizeTestStrategy], along with the
  /// mixin [ResynthesizeTestHelpers].
  mixin ResynthesizeTestCases implements ResynthesizeTestHelpers {
    static final FeatureSet featureSetLegacy = FeatureSet.fromEnableFlags2(
      sdkLanguageVersion: Version.parse('2.9.0'),
      flags: [],
    );
  
    static final FeatureSet featureSetNullSafe = FeatureSet.fromEnableFlags2(
      sdkLanguageVersion: Version.parse('2.12.0'),
      flags: [],
    );
  
    test_class_abstract() async {
      var library = await checkLibrary('abstract class C {}');
  