Unit Testing Concurrent Code

Question

My weekend project consists of writing a cross-platform concurrency primitives library (critical sections, read/write mutexes, interlocked integers, events, etc) and was wondering how to unit test this stuff. I realize that testing concurrent code is hard in itself, but testing the primitives of said code couldn't be that hard, could it?

Turns out, it is that hard. At least, for me it is.

So how would you go about approaching this? Just as an example, I don't even know where to start with testing critical sections.

Answer 1

Don't think about unit tests, think about the behaviour you want to specify. For example:

Given_an_unlocked_lock
    It_should_be_possible_to_take_it
Given_a_locked_locked
    It_should_not_be_possible_to_take_it_from_another_thread
    It_should_be_possible_take_it_from_the_same_thread
Given_a_locked_locked_when_unlocked
    It_should_be_possible_to_take_it
Given_a_locked_locked_when_owning_thread_terminates
    It_should_be_possible_to_take_it

I think that will help you identify what to do. And yes probably you need a helper thread in your unit tests to make it happen. Maybe this example is helpful.