title: How do I mock callbacks on a ref for testing in react?
body: <p>I am using video-react in a react application. I have to test a component that calls ref methods from a video-react component.
  I hope to use enzyme so I can mount the component and check that I have called the ref method in ComponentDidMount.</p>
  
  <p>Basically, how do I test that refs.player.seek gets called like it does below?</p>
  
  <pre><code>componentDidMount() {
      this.refs.player.seek(this.props.currentTime);
      this.refs.player.subscribeToStateChange(this.handlePlayerStateChange);
  }
  </code></pre>