Even if its subject to change, I think we should be doing unit tests, as you never know, it might never change.

Good question about the graphical implementation details. In this case I think that show/hide (like possibly mute/unmute) verges on the functional side of things rather than graphical display - e.g. if we're not showing a button, or we're hiding a video, then that's really bad for the user. If we just have a bad layout, then that's slightly different.

So I think I would tend towards having a unit test for show/hiding things.