anchor.diff:          .build();
         var tracker = new RequestTrackingTransformer();
         var handler = bareHandler.transformResponses(tracker);
  -      
  +
         var x = ' ';
         tracker.trackingStream.listen(expectAsync1((event) {
           expect(event.request, equals(TEST_GET_REQUEST));
  
positive.code:         }));
        }));
        handler.handle(TEST_GET_REQUEST).listen(expectAsync1((entity) {
          print("Inside callback: $entity");
          x = entity['x'];
        }, count: 2));
      });
  
negative.code:         .build();
        var tracker = new RequestTrackingTransformer();
        var handler = bareHandler.transformResponses(tracker);
  
        tracker.trackingStream.listen(expectAsync1((event) {
          expect(event.request, equals(TEST_GET_REQUEST));
          event.onFirstResponse.catchError(expectAsync1((error) {
  