anchor.diff:  :marked
     ### Test it
     
  -  Tests click buttons of both the parent `MissionControlComponent` and the `AstronoutComponent` children
  +  Tests click buttons of both the parent `MissionControlComponent` and the `AstronautComponent` children
     and verify that the *History* meets expectations:
     
   +makeExample('cb-component-communication/e2e-spec.js', 'bidirectional-service')
  
positive.code:     it controls the lifetime of the `MissionService`.
  :marked
    The *History* log demonstrates that messages travel in both directions between
    the parent `MissionControlComponent` and the `AstronoutComponent` children,
    facilitated by the service:
    
  figure.image-display
  
negative.code: +makeExample('cb-component-communication/ts/app/missioncontrol.component.ts')
  
  :marked
    The `AstronautComponent` also injects the service in its constructor.
    Each `AstronautComponent` is a child of the `MissionControlComponent` and therefore receives its parent's service instance:
    
  +makeExample('cb-component-communication/ts/app/astronaut.component.ts')
  
  