This assertion is kind of unnecessary--the point of the test (right now) is to ensure that the `waitsFor` call did not time out. Is there any other user-facing state change in response to a thumbnail selection? I'm not set up to develop on the Video application (my phone requires an SD card to do anything with the application), so I can't make any concrete recommendations.

If not, then it probably makes sense to delete this test altogether. By encapsulating the `waitsFor` inside the function itself ([as I recommended above](https://github.com/mozilla-b2g/gaia/pull/12717/files#r7942061)), this expectation will be implicitly asserted every time you use the `app.clickThumbnail` method.