anchor.diff:    Consider also the [_fakeAsync_](#fake-async) alternative which affords a more linear coding experience.
     
     在一个测试（比如`fixture.whenStable`）里面调用函数时，会继续体现它们的异步行为。
  -  考虑使用[_fakeAsync_](#fake-async)，以获得一个更加直观的代码经验。
  +  考虑使用[_fakeAsync_](#fake-async)，以获得更加直观的代码经验。
   
   #when-stable
   :marked
  
positive.code:   There can be injectors at multiple levels, from the root injector created by the `TestBed`
    down through the component tree.
  
    Angular有一个层次化的注入系统。
    可以有很多层注入器，从根`TestBed`创建的注入器下来贯穿整个组件数。  
  
    The safest way to get the injected service, the way that **_always works_**, 
  
negative.code:   that hides the mechanics of asynchronous execution, just as it does when passed to an [_it_ test)(#async).
  
    注意`beforeEach`里面对`async`的调用。
    `async`函数将测试代码安排到一个特殊的**异步测试区域**来运行，该区域隐藏了异步执行的细节，就像它被传递给[_it_ 测试)(#async)一样。
  
  #compile-components
  :marked
  