title: Test functions cannot both take a 'done' callback
body: <p>I'm trying to create a simple test with nestjs, and I'm getting this error</p>
  <blockquote>
  <p>Test functions cannot both take a 'done' callback and return something. Either use a 'done' callback, or return a promise.</p>
  <p>Returned value: Promise {}</p>
  </blockquote>
  <p>The unit test is so simple, but I get an error when I use done();</p>
  <pre><code>it('throws an error if a user signs up with an email that is in use', async (done) =&gt; {
  fakeUsersService.find = () =&gt; Promise.resolve([{ id: 1, email: 'a', password: '1' } as User]);
  try {
    await service.signup('asdf@asdf.com', 'asdf');
  } catch (err) {
    done();
  }
  });
  </code></pre>