anchor.diff:    Neither test can prove that a value from the service is be displayed.
     The quote itself has not arrived, despite the fact that the spy returns a resolved promise.
     
  -  两者都不能证明被显示的值是从服务的。
  +  两者都不能证明被显示的值是服务提供的。
     虽然spy返回了解析的承诺，名言本身还没有到来。
     
     This test must wait at least one full turn of the JavaScript engine before the
  
positive.code:   The `ComponentFixture.whenStable` method returns its own promise which resolves when the `getQuote` promise completes.
    In fact, the _whenStable_ promise resolves when _all pending asynchronous activities within this test_ complete ... the definition of "stable".
  
    `ComponentFixture.whenStable`方法返回它自己的承诺，它在`getQuote`承诺完成时被解析。实际上，当**所有待处理异步行为**完成时即为“stable”，在“stable”后**whenStable**承诺被解析。
  
    Then the test resumes and kicks off another round of change detection (`fixture.detectChanges`)
    which tells Angular to update the DOM with the quote.
  
negative.code:   This test has no direct access to the promise returned by the call to `testService.getQuote` 
    which is private and inaccessible inside `TwainComponent`.
  
    调用`testService.getQuote`返回的承诺是私有的，不能在`TwainComponent`内访问，这个测试程序也对其无访问权。
  
    Fortunately, the `getQuote` promise is accessible to the _async test zone_ 
    which intercepts all promises issued within the _async_ method call.
  