title: Test Observable that is piped and uses async pipe
body: <p>I have the following situation. I have an Observable, <code>myObservable$</code> initialized in <code>ngOnInit</code>. When that happens, the observable is tapped to copy the last value for other purposes. Aside from that, the observable is bound to something my html using the <code>async</code> pipe. How can I test that my tapped function is happening correctly, using jasmine karma?</p>
  <p>html:</p>
  <pre><code>&lt;input [ngModel]=&quot;myObservable$ |async&quot;&gt;
  </code></pre>
  <p>ts:</p>
  <pre><code>ngOnInit():void {
      this.myObservable$ = this.service.getThings()
        .pipe(tap(value=&gt;this.otherProperty=value))
  }
  </code></pre>
  <p>I want to test, in this instance, that <code>this.otherProperty</code> actually has the value. How can I test this?</p>