title: Failing expect() inside subscribe() does not mark test as invalid
body: <p>We recently upgraded to Angular 6.0.3, RxJs 6.2.0 and jest 23.1.0 (upgrading from RxJS 5 &amp; Angular 4). </p>
  
  <p>There seems to be a problem with Jest &amp; RxJs as failing expect-statements inside a subscribe-Block do not mark the test as failed. Here's a minimal example:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>    it("should fail", () =&gt; {
  
          const obs = Observable.create((observer) =&gt; {
              observer.next(false);
          });
  
          obs.subscribe((value) =&gt; {
              console.log(value); // =&gt; false
              expect(value).toBeTruthy();
          });
  
      });</code></pre>
  </div>
  </div>
  </p>
  
  <p>The expect-Statement gets executed, but the test still passes. We didn't observe this behaviour with the previous RxJs version and Jest.</p>