anchor.diff:            expect(machine.current, stateA);
             log.add('a');
             stateB.enter();
  -        }) as Callback1);
  +        }));
       stateB.onFuture(
           new Future.delayed(new Duration(milliseconds: 1)),
           expectAsync1((value) {
             expect(log, ['a']);
             expect(value, isNull);
  -        }) as Callback1);
  +        }));
   
       machine.start();
     });
  
positive.code:         expectAsync0(() {
            expect(machine.current, stateA);
            stateB.enter();
          }) as Callback0);
      stateA.onTimeout(
          new Duration(milliseconds: 20),
          () => fail('should never be called'));
  
negative.code:         expectAsync0(() {
            expect(machine.current, stateB);
            stateC.enter();
          }));
  
      machine.start();
    });
  