title: AnimationEvent is not defined in Jest
body: <p>I'm trying to mock an <code>animationEvent</code> for one of my test in an Angular app and I'm getting an error:</p>
  <blockquote>
  <p>ReferenceError: AnimationEvent is not defined.</p>
  </blockquote>
  <p>I'm assuming that as this is an experimental feature it won't be available in jsdom in Jest. Does anyone know a way to mock this?</p>
  <p>This is the code that is failing</p>
  <pre><code>dispatchEvent(new AnimationEvent(&quot;animationend&quot;, { animationName: &quot;slide-down&quot; }));
  </code></pre>
  <p>Does anyone know how to get around this?</p>
  <p>This event will trigger some code in my component and will emit an output event itself, but I want to make sure that this happens when this specific type of event with the <code>animationName</code> 'slide-down' happens.</p>