title: Angular test: override to use template instead of templateUrl
body: <p>I have a component which contains <code>iframe</code>. To prevent loading not existing URL from iframe in tests I would like to mock component's template. I thought I could do it using <code>TestBed.overrideComponent()</code> but it has no effect. When test runs I can see the original template is present and iframe loads non-existing url.</p>
  
  <p>What I tried:</p>
  
  <pre><code>fixture = TestBed.overrideComponent(IFrameComponent, {
    remove: {
      templateUrl: './iframe.component.html'
    },
    add: {
      template: '&lt;div&gt;&lt;/div&gt;'
    }
  }).createComponent(IFrameComponent);
  </code></pre>
  
  <p>How can I override component to use <code>template</code> instead of <code>templateUrl</code>?</p>