title: Async tests with Jest (without Promises)
body: <p>Is there a way to test something like this with Jest:</p>
  
  <pre class="lang-js prettyprint-override"><code>function hello(callback) {
    someNonPromiseBasedAPI(callback);
  }
  </code></pre>
  
  <p>Something like <code>done()</code>/<code>waitsFor()</code> in Jasmine</p>
  
  <p>The Jest documentation states that to test an async function it must return a Promise but I don't want to modify my code to suit the test.</p>