java - 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 Hard (TM)" and "It Depends (TM)". So I thought that reducing the scope of the question would be more useful.

Background : We are implementing a simple scheduler that gives you a way to register callbacks when starting and stopping jobs and of course configure the frequency of scheduling. Currently, we're making a lightweight wrapper around java.util.Timer.

Aspects:

• I haven't found a way to test this scheduler by relying on only public interfaces (something like addJob(jobSchedule, jobArgs,jobListener) , removeJob(jobId)).

• How do I time the fact that the the job was called according to the schedule specified ?

Answer 1

you could use a recorder object that record the order, timings and other useful stuff in each unit test of your scheduler. The test is simple:

1. create a recorder object
2. configure the schedule
3. execute a unit test
4. check that recorder object is "compatible" with the schedule