title: Test that function was called inside subscribe
body: <p>I need to check that my <code>save()</code> function was called like shown below. I'm having trouble getting the subscribe to be called so I can check that my <code>saveSpy</code> was called.</p>
  <p><strong>some.component.ts</strong></p>
  <pre><code> ionViewWillEnter() {
      this.someService.someSubscription =
        this.someService.someAction.subscribe(() =&gt; {
          this.save();
        });
    }
  </code></pre>
  <p><strong>some.component.spec.ts</strong></p>
  <pre><code>  it('should set someSubscription on ionViewWillEnter', fakeAsync(() =&gt; {
      spyOn(component['someService'], 'someAction').and.callThrough();
      const saveSpy = spyOn(component, 'save');
      component.ionViewWillEnter();
      flush();
      expect(saveSpy).toHaveBeenCalled();
    }));
  </code></pre>
  <p><code>TypeError: this.someService.someAction.subscribe is not a function</code></p>