Library for Asserting Multi Thread Code in Java

Question

As a TDD practitioner I want to test everything I code.

During the last couple of years I've been coding many multithreaded code and one part of my tests have been bothering very much.

When I have to assert something that may happen during the run() loop i end up with some kind o assertion like this:

assertEventually(timeout, assertion)

I know that Mockito has a solution for this, but only for the verify call. I know also that JUnit has a timeout property that is useful to avoid hanging (or ever lasting) tests. But what I want is something that allows me to assert something that may become true over time.

So my question is, does anyone knows a library that provides this?

Here is my solution so far:

private void assertEventually(int timeoutInMilliseconds, Runnable assertion){
    long begin = System.currentTimeMillis();
    long now = begin;
    Throwable lastException = null;
    do{
        try{
            assertion.run();
            return;
        }catch(RuntimeException e){
            lastException = e;
        }catch(AssertionError e){
            lastException = e;
        }
        now = System.currentTimeMillis(); 
    }while((now - begin) < timeoutInMilliseconds);
    throw new RuntimeException(lastException);
}

Using it ends up like this:

assertEvetuallyTrue(1000, new Runnable() {
        public void run() {
            assertThat(Thread.activeCount()).isEqualTo(before);
        }
    });

Answer 1

Two libraries you may want to check out:

• ConcurrentUnit - allows you to perform assertions from any thread, waiting a fixed amount of time
• Awaitility - allows you to wait a fixed amount of time or until some condition is satisfied