@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);
}