anchor.diff:    covariant num foo;
   }
   class C extends A {
  -  covariant @virtual num foo;
  +  covariant num foo;
   }
   class D extends C {
  -  @virtual int foo;
  +  int foo;
   }
   class E extends D {
  -  @virtual num foo;
  +  num foo;
   }
       ''');
     }
  
positive.code: }
  ''');
    }
  
    void _addMetaLibrary() {
      addFile(r'''
  library meta;
  class _Checked { const _Checked(); }
  const Object checked = const _Checked();
  
  class _Virtual { const _Virtual(); }
  const Object virtual = const _Virtual();
      ''', name: '/meta.dart');
    }
  }
  
negative.code:   final ToVoid<dynamic> g = null;
  }
   ''');
    }
  
    test_fieldSetterOverride() async {
  