    @Test
    public void testFlowWithFixedThreadPool() throws Exception {

        pool = Executors.newFixedThreadPool(POOL_SIZE);

        List<CompletableFuture<Integer>> futures = new ArrayList<>();

        for (int i = 0; i < 20; i++) {
            futures.add(
                    CompletableFutureFlow.flowWithId(i, pool));
        }

        futures.forEach(CompletableFutureFlow::getFuture);
    }