public static SharedScheduledExecutorService getSingleThreadExecutor() {
        setup();
        return singleThreadExecutor;
    }
@Test
    public void singleThread() {
        ScheduledExecutorService a = SharedScheduledExecutors.getSingleThreadExecutor();
        assertNotNull("ScheduledExecutorService must not be null", a);
        ScheduledExecutorService b = SharedScheduledExecutors.getSingleThreadExecutor();
        assertSame("factories should be same", a, b);
    }