Ensure that assertion failures don’t cause deadlocks
Make a test less dependent on the sequence of events

This test depends on the callbacks of futures being called in the same order they were registered in, which is not guaranteed by the API. It doesn’t need to assert the order, it only needs to assert that the two things happened (really only that the reactor restarted, but it feels good to show that it also crashed).
Wait until the first tick before checking if the reactor has started