Gist.java

@Test
public void threadsShouldBePresentBeforeKeepAliveTimeKicks() throws Throwable {
    CountDownLatch untilAllThreadsDone = startaBunchOfThreads();

    untilAllThreadsDone.await();

    waitBeforeTimeoutOccurs();

    assertEquals(countExecutorThreads(), threadPoolSize);
}

private void waitBeforeTimeoutOccurs() throws InterruptedException {
    Thread.sleep(timeoutMillis / 2);
}