anchor.diff:  
   @JS('React.addons.TestUtils.Simulate')
   external dynamic get _Simulate;
  -
   
   void _typedCallbackRefTests<T>(react.ReactComponentFactoryProxy factory) {
     if (T == dynamic) {
  
positive.code:   group('forwardRef wraps event handlers properly,', () {
      final isDartComponent = factory is ReactDartComponentFactoryProxy;
  
      const dartInside = EventTestHelper.dart('onMouseDown', 'inside forwardRef');
      const dart = EventTestHelper.dart('onMouseUp', 'set on forwardRef hoc');
      const dartCloned = EventTestHelper.dart('onMouseLeave', 'cloned onto forwardRef hoc');
      const jsCloned = EventTestHelper.js('onClick', 'cloned onto forwardRef hoc ');
      const helpers = {dartInside, dart, jsCloned, dartCloned};
  
      Element node;
      Map<EventTestHelper, dynamic> events;
      Map propsFromDartRender;
  
      setUpAll(() {
        expect(helpers.map((h) => h.eventPropKey).toSet(), hasLength(helpers.length),
            reason: 'test setup: each helper should have a unique event key');
  
        node = null;
  
negative.code:     if (isDartComponent) {
        group('in a way that the handlers are callable from within the Dart component:', () {
          setUpAll(() {
            expect(propsFromDartRender, isNotNull,
                reason: 'test setup: component must pass props into props.onDartRender');
          });
  
          final dummyEvent = react.SyntheticMouseEvent(null, null, null, null, null, null, null, null, null, null, null,
              null, null, null, null, null, null, null, null, null, null, null, null, null, null, null);
  
          for (var eventCase in eventCases.where((helper) => helper.isDart)) {
            test(eventCase.description, () {
              expect(() => propsFromDartRender[eventCase.eventPropKey](dummyEvent), returnsNormally);
            });
          }
        });
  