What are some strategies to unit test a scheduler?

Question

This post started out as \"What are some common patterns in unit testing multi-threaded code ?\", but I found some other discussions on SO that generally agreed that \"It is

Answer 1

There are many failure modes that such a scheduler could exhibit, and each would most likely require its own test case. These test cases are likely to be very different, so "it depends."

For testing concurrent software in Java in general, I recommend this presentation from JavaOne 2007: Testing Concurrent Software.

For testing that a scheduler must execute jobs in accurate accordance to their schedule, I'd create an abstraction of time itself. I've done something similar in one of my projects, where I have a Time or Clock interface. The default implementation will be MillisecondTime, but during testing I will switch it out with a TickTime. This implementation will allow my unit test to control when the time advances and by how much.

This way, you could write a test where a job is scheduled to run once every 10 tick. Then your test just advances the tick counter and checks to make sure that the jobs run at the correct ticks.