How do I write a Junit test for a ThreadPoolExecutor

Question

How can I write a Junit test for the following function. ParallelExecutor extends ThreadPoolExecutor and the WorkerThread will call latch.countDown() on a value change(listener). WorkerThread is a 3 party class. Please let me know how I can tell the test to decrease the latch.

    public static void OpenScreen() throws InterruptedException {
//some job...3 party screen
    // creating the ThreadPoolExecutor
    final ParallelExecutor executorPool = new ParallelExecutor(10);
    final CountDownLatch latch = new CountDownLatch(0);
    // start the monitoring thread
    final MyMonitorThread monitor = new MyMonitorThread(executorPool, 3);
    final Thread monitorThread = new Thread(monitor);
    monitorThread.start();
    // monitorThread.start();
    // submit work to the thread pool
    for (int i = 0; i < 10; i++) {
        executorPool.execute(new WorkerThread(("cmd" + i), latch));
    }

    latch.await();
    Thread.sleep(30000);
    // shut down the pool
    executorPool.shutdownNow();
    // shut down the monitor thread
    monitor.shutdown();

}

Answer 1

So what do you want to test? :-) That the execute methods are called? The counting works? Timeouting works if one of the tasks take too much to execute? All the jobs completed when the openScreen() method returns?

If you want to do unit tests, you can play around with mocks (for that, I'd extract this functionality to a separate class where the dependencies like the pool and monitor are passed/injected for the new class). There you can verify if the methods were called properly.