@Test
    public void zipWith() { // this test failed
        AtomicInteger i = new AtomicInteger(0);
        Tuple2<Integer, Integer> res = Mono.just(1)
                .filter(x -> x == 0)
                .<Integer>zipWith(Mono.create(s -> {
                    i.incrementAndGet();
                    s.success(5);
                }))
                .block();
        Assert.assertNull(res);
        Assert.assertEquals(0, i.get());
    }

    @Test
    public void zipWhen() {
        AtomicInteger i = new AtomicInteger(0);

        Tuple2<Integer, Integer> res = Mono.just(1)
                .filter(x -> x == 0)
                .<Integer>zipWhen(x -> Mono.create(s -> {
                    i.incrementAndGet();
                    s.success(5);
                }))
                .block();
        Assert.assertNull(res);
        Assert.assertEquals(0, i.get());
    }