Make Mocha Wait for UI to Update

I'm using Mocha and Chai as part of the web-component-tester tool to write my tests. As part of those tests, I need to wait for a part of the UI to update before doing an assertion.

The only way I've been able to figure out how to do this successfully is by using a timeout:

test("should update image", function(done) {
  setTimeout(function() {
      assert.equal(document.querySelector(".tp-revslider-mainul .tp-revslider-slidesli:nth-child(1) .tp-bgimg").getAttribute("src"), "https://someurl/image.jpg");
      done();
  }, 5000);
});

Is there a better way? CasperJS has a waitFor function that is great in situations like these, but I'm not sure how to do the same in Mocha.

Thx.