@Test
  public void testDelayErrorMaxConcurrent() {
    final List<Long> requests = new ArrayList<>();
    Observable<Integer> source =
        Observable.mergeDelayError(
            Observable.just(
                    Observable.just(1).asObservable(),
                    Observable.<Integer>error(new TestException()))
                .doOnRequest(
                    new LongConsumer() {
                      @Override
                      public void accept(long t1) {
                        requests.add(t1);
                      }
                    }),
            1);

    TestSubscriber<Integer> ts = new TestSubscriber<>();

    source.subscribe(ts);

    ts.assertValue(1);
    ts.assertTerminated();
    ts.assertError(TestException.class);
    assertEquals(Arrays.asList(1L, 1L, 1L), requests);
  }