Ultimately we decided we couldn't do true black-box testing. With a test like this we can go three ways:
(1) if the test is _trivial_ (the value isn't cached and isn't calculated) then we don't bother keeping it
(2) if the test is calculated but not cached, then we keep the test in the form this one is
(3) (this is the case for this test) if the test is cached, then we reset the cached status between calls, if possible, and test the combination of check-reset. Here, setting the source of the player back to animation voids the cancel, so doing that after player.cancel() would be appropriate.