anchor.diff:    <a href="https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Getting_started/Selectors" target="_blank">standard CSS selector</a>
     predicate that filters the same way as a jQuery selector.
   
  +  **`By`**类是一个Angular测试工具，它生成有用的predicate。
  +  它的`By.css`静态方法产生一个<a href="https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Getting_started/Selectors" target="_blank">标准CSS选择器</a>
  +  predicate，与JQuery选择器相同的方式过滤。
  +
     Finally, the setup assigns the DOM element from the `DebugElement` **`nativeElement`** property to `el`.
     The tests will assert that `el` contains the expected title text.
   
  +  最后，这个配置指定`DebugElement`中的**`nativeElement`DOM元素到属性`el`。
  +  测试将判断`el`是否包含期待的标题文本。
   
     ### The tests
  +  ### 测试
  +
     Jasmine runs the `beforeEach` function before each of these tests
  +
  +  再每个测试之前，Jasmin都一次运行`beforeEach`函数：
  +
   +makeExample('testing/ts/app/banner.component.spec.ts', 'tests', 'app/banner.component.spec.ts (tests)')(format='.')
   :marked
     These tests ask the `DebugElement` for the native HTML element to satisfy their expectations.
  
positive.code:     - 显示`Karma`的浏览器窗口（之前被隐藏了）。
      
      - Click the "DEBUG" button; it opens a new browser tab and re-runs the tests
      
      - Open the browser's “Developer Tools” (F12 or Ctrl-Shift-I).
  
  
negative.code:   But it only works when Angular injects the component with the service instance in the test's root injector.
    Fortunately, in this test suite, the _only_ provider of `UserService` is the root testing module, 
    so it is safe to call `TestBed.get` as follows:
  
    你**可以**通过`TestBed.get`方法来从根注入器中获取服务。
    它更容易被记住，也更加简介。
    But it only works when Angular injects the component with the service instance in the test's root injector.
    Fortunately, in this test suite, the _only_ provider of `UserService` is the root testing module, 
    so it is safe to call `TestBed.get` as follows:
    
  +makeExample('testing/ts/app/welcome.component.spec.ts', 'inject-from-testbed', 'TestBed injector')(format='.')
  .l-sub-section
    :marked
  