Avoid timing-sensistive sleeps in test code

[Sushisource]

We have a handful of tests that require sleeps to get things to happen in an expected order. This is obviously not ideal. We need a reasonable way to wait for certain things to happen deep in the internals of the code and expose that to tests in a way that doesn't require making all sorts of ugly changes purely for that ability.

If we could leverage tracing for this, that'd be nice. We could just wait to see some specific event in the test.