test.py

def test_task_completed_arrived_before_task_started():
    # First of all, send a task_completed event
    _send_task_completed_event()

    # Now wait a bit, and send a task_started event
    time.sleep(3)
    _send_task_started_event()

    completed = False
    with time_limit(MAX_RETRY_COUNT * 10):  # Limit the time the test can run
        while not completed:
            time.sleep(5)
            task = _get_task_from_db()
            if task.is_completed:
                completed = True
                assert task.started_at < task.completed_at  # Verify the processing order of events
    assert completed