CountDownLatch等待超时在测试用例中不起作用

Question

我为asyncTask编写了一个测试用例，如下所示。我发现无论我在CountDownlatch等待中使用什么超时，情况仍然可以通过。甚至比asyncTask中的睡眠时间还短。

有人可以启发我，为什么等待不超过超时抛出异常吗？

public class MyAsyncTask extends AsyncTask<Void, Void, Integer> {

    @Override
    protected Integer doInBackground(Void... voids) {
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return 3;
    }
}

@RunWith(RobolectricTestRunner.class)
public class MyAsyncTaskTest {
    @Test
    public void doInBackground_shouldCompleteInTime() throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(1);
        MyAsyncTask task = new MyAsyncTask() {
            @Override
            protected void onPostExecute(Integer integer) {
                assertThat(integer).isEqualTo(3);
                latch.countDown();
            }
        };

        task.execute();
        latch.await(100, TimeUnit.MILLISECONDS); // not throw exception, why?

        assertThat(latch.getCount()).isEqualTo(0);
    }
}