How do I perform a Unit Test using threads? [duplicate]

Answer 1

Implement a UncaughtExceptionHandler that sets some flags (which the Threads peridocially check) and set it on each Thread.

Answer 2

Your runnable wrapper should be passing the exception object back to your test class and then you can store them in a collection. When all the tests are finish you can test the collection. If it isn't empty, iterate over each of the exceptions and .printStackTrace() then fail.

Answer 3

It is possible making the unit test to fail, by using a special synchronization object. Take a look at the following article: Sprinkler - Advanced synchronization object

I'll try to explain the main points here. You want to be able to externalize internal threads failures to the main thread, which, in your case is the test. So you have to use a shared object/lock that both the internal thread and the test will use to sync each other. See the following test - it creates a thread which simulates a thrown exception by calling a shared object named Sprinkler. The main thread (the test) is blocked on Sprinkler.getInstance().await(CONTEXT, 10000) which, by the time release is called - will be free and catch the thrown exception. In the catch block you can write the assert which fails the test.

 @Test
    public void testAwait_InnerThreadExternalizeException() {

        final int CONTEXT = 1;
        final String EXCEPTION_MESSAGE = "test inner thread exception message";

        // release will occur sometime in the future - simulate exception in the releaser thread
        ExecutorServiceFactory.getCachedThreadPoolExecutor().submit(new Callable<void>() {

            @Override
            public Void call() throws Exception {

                Sprinkler.getInstance().release(CONTEXT, new RuntimeException(EXCEPTION_MESSAGE));

                return null;
            }

        });

        Throwable thrown = null;
        try {
            Sprinkler.getInstance().await(CONTEXT, 10000);
        } catch (Throwable t) {
            // if the releaser thread delivers exception it will be externelized to this thread
            thrown = t;
        }
        Assert.assertTrue(thrown instanceof SprinklerException);
        Assert.assertEquals(EXCEPTION_MESSAGE, thrown.getCause().getMessage());
    }

Answer 4

The Google Testing Blog had an excellent article on this subject that's well worth reading: http://googletesting.blogspot.com/2008/08/tott-sleeping-synchronization.html

It's written in Python, but I think the principles are directly transferable to Java.

Answer 5

Unit testing in a multithreaded environment is tough... so some adjustments need to be made. Unit tests must be repeatable.. deterministic. As a result anything with multiple threads fails this criteria. Tests with multiple threads also tend to be slow.

• I'd either try to see if I can get by with testing on a single thread.. does the logic under test really need multiple threads.
• If that doesn't work, go with the member variable approach that you can check against an expected value at the end of the test, when all the threads have finished running.

Hey seems like there's another question just like this. Check my post for a link to a longer discussion at the tdd yahoogroup Unit testing a multithreaded application?

Answer 6

Concurrency is one of those things that are very difficult to unit test. If you are just trying to test that the code inside each thread is doing what it is supposed to test, may be you should just test this code isolated of the context. If in this example the threads collaborate to reach a result, may be you can test that collaboration without using threads. That would be done by executing all the collaborative parts sequentially. If you want to test for race conditions and these kind of things, unit testing is not the best way. You will get tests that sometimes fail and sometimes don´t fail. To summarize, I think that may be your problem is that you are unit testing in a level too high. Hope this helps