@Test
public void testGetSequenceId() throws InterruptedException {

    ExecutorService es = Executors.newFixedThreadPool(5);
    ConcurrentHashMap<Long, String> set = new ConcurrentHashMap<>();
    for (AtomicInteger i = new AtomicInteger(0); i.get() < 1000000; i.incrementAndGet()) {
        es.submit(() -> {
            long s1 = SequenceGenerator.getSequenceId("A");
            set.put(s1, "");
        });
    }
    TimeUnit.SECONDS.sleep(5);
    assertEquals(1000000, set.size());
}