// Poll from empty queue should return null
        final OpenSearchUrlQueue result = urlQueueService.poll(sessionId);
        assertNull(result);
    }

    @Test
    public void test_poll_singleItemTx() {
        final String sessionId = "poll_session2";
        final OpenSearchUrlQueue urlQueue = new OpenSearchUrlQueue();
        urlQueue.setCreateTime(System.currentTimeMillis());
        urlQueue.setDepth(1);