Concurrent JUnit testing

Question

I have a large JUnit test suite, where I'd quite like to run all the tests concurrently for two reasons:

• Exploit multiple cores to run the whole test suite faster
• Hopefully detect some errors due to non-thread-safe global objects

I recognise that this will force me to refactor some code to make it thread-safe, but I consider that to be a good thing :-)

What's the best way to get JUnit to run all the tests concurrently?

Answer 1

Are you fixed to JUnit? TestNG provides good multi thread testing out of the box and it's compatible with JUnit tests (you need to make a few changes). For example you could run a test like this:

@Test(threadPoolSize = 3, invocationCount = 9,  timeOut = 10000) public void doSomething() { ... } 

This would mean that the doSomething() method will be invoked 9 times by 3 different threads.

I highly recommend TestNG.

Answer 2

I was looking for an answer to exactly this question, and based on the answers here, and what I read elsewhere, it appears as if there isn't currently an easy out-of-the-box way to run existing tests in parallel using JUnit. Or if there is I didn't find it. So I wrote a simple JUnit Runner that accomplishes that. Please feel free to use it; see http://falutin.net/2012/12/30/multithreaded-testing-with-junit/ for a complete explanation and the source code of the MultiThreadedRunner class. With this class, you can just annotate your existing test class(es) like this:

@RunWith(MultiThreadedRunner.class)