title: Cannot read property 'subscribe' of undefined after running npm test (Angular 2 unit testing)
body: <p>I've created a testing (spec) file for a component I'm testing. But when I run the test, it gives me an error saying </p>
  
  <pre><code>Cannot read property 'subscribe' of undefined
  TypeError: Cannot read property 'subscribe' of undefined
  at ComponentUndertest.ngOnInit
  </code></pre>
  
  <p>which is obvious because I have subscribed to something in my ngOnInit() method, but can I ignore the subscription during the test? Or can I fake a subscription during testing?
  I have googled a lot about this issue but couldn't find anything related with angular2 testing.
  Thanks in advance.</p>