Question

Does anyone have any advice for a consistent way to unit test a multithreaded application? I have done one application where our mock ‘worker threads’ had a thread.sleep with a time that was specified by a public member variable. We would use this so we could set how long a particular thread would take to complete its work, then we could do our assertions. Any ideas of a better way to do this? Any good mock frameworks for .Net that can handle this?

Answer 1

My advice would be not to rely on unit tests to detect concurrency issues for several reasons:

• Lack of reproducibility: the tests will fail only once in a while, and won’t be really helpful to pinpoint the problems.
• Erratic failing build will annoy everybody in the team – because the last commit will always be wrongly suspected for being the cause of the failing build.
• Deadlocks when encountered are likely to freeze the build until the execution timeout is encountered which can significantly slow down the build.
• The build environment is likely to be a single CPU environment (think build being run in a VM) where concurrency issues may never happen – no matter how much sleeping time is set.
• It defeats somehow the idea of having simple, isolated units of validating code.