title: Angular2 unit testing : testing a component's constructor
body: <p>All is in the title : <strong>how can one test what is done in the component's constructor ?</strong></p>
  
  <p>For your information, I am using a service that requires a setting, and I would like to see if the 2 methods that I call in the constructor are called correctly. </p>
  
  <p>My component's constructor : </p>
  
  <pre><code>constructor(
    public router: Router,
    private profilService: ProfileService,
    private dragula: DragulaService,
    private alerter: AlertService
  ) {
    dragula.drag.subscribe((value) =&gt; {
      this.onDrag(value);
    });
    dragula.dragend.subscribe((value) =&gt; {
      this.onDragend(value);
    });
  }
  </code></pre>