In the context of diffusion pipelining, it is important that tentative followers promptly emit an instruction to roll forward after the tentative header got set. We check this behavior by comparing the timestamps when a tentative header got set and when a tentative follower emits an instruction containing it.

This test is making use of io-sim to measure and check the *exact* timings of various events. In particular, we can really rely on something occuring at a specific point in time, compared to just a plausible range as would be necessary with ordinary wall-clock time.