anchor.diff:  
   .l-hr
   
  -a#atp-api
  +#atp-api
   :marked
     # Angular Testing Platform APIs
   
  
positive.code: 
  .l-hr
  
  a#isolated-tests
  a#testing-without-atp
  :marked
    # Testing without the Angular Testing Platform
  
  
negative.code:   By now you know how to stub the `Router` and a data service.
    Stubbing the `ActivatedRoute` would follow the same pattern except for a complication:
    the `ActivatedRoute.params` is an _Observable_.
  #stub-observable
  :marked
    ### _Observable_ test double
  
  