synchronized void appendRecheckOp() {
        doAppend(RECHECK_OP);
    }
@Test
    public void testRecheckTask() {
        QueueInstance instance = createInstance();

        for (int i = 0; i < 10; i++) {
            instance.queue.appendRecheckOp();
        }

        Awaitility.await().untilAsserted(() -> {
            verify(instance.mockedConsumer, times(10)).recheckTopicsChange();
        });

        // cleanup.
        instance.close();
    }