@Test
  public void testErrorInParentObservableDelayed() throws Exception {
    for (int i = 0; i < 50; i++) {
      final TestASynchronous1sDelayedObservable o1 = new TestASynchronous1sDelayedObservable();
      final TestASynchronous1sDelayedObservable o2 = new TestASynchronous1sDelayedObservable();
      Observable<Observable<String>> parentObservable =
          Observable.create(
              new Publisher<Observable<String>>() {
                @Override
                public void subscribe(Subscriber<? super Observable<String>> op) {
                  op.onSubscribe(EmptySubscription.INSTANCE);
                  op.onNext(Observable.create(o1));
                  op.onNext(Observable.create(o2));
                  op.onError(new NullPointerException("throwing exception in parent"));
                }
              });

      Subscriber<String> stringObserver = TestHelper.mockSubscriber();

      TestSubscriber<String> ts = new TestSubscriber<>(stringObserver);
      Observable<String> m = Observable.mergeDelayError(parentObservable);
      m.subscribe(ts);
      System.out.println("testErrorInParentObservableDelayed | " + i);
      ts.awaitTerminalEvent(2000, TimeUnit.MILLISECONDS);
      ts.assertTerminated();

      verify(stringObserver, times(2)).onNext("hello");
      verify(stringObserver, times(1)).onError(any(NullPointerException.class));
      verify(stringObserver, never()).onComplete();
    }
  }
  @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);
  }
 @Test
 public void testErrorInParentObservable() {
   TestSubscriber<Integer> ts = new TestSubscriber<>();
   Observable.mergeDelayError(
           Observable.just(Observable.just(1), Observable.just(2))
               .startWith(Observable.<Integer>error(new RuntimeException())))
       .subscribe(ts);
   ts.awaitTerminalEvent();
   ts.assertTerminated();
   ts.assertValues(1, 2);
   assertEquals(1, ts.errorCount());
 }
  @Test
  public void testScanWithRequestOne() {
    Observable<Integer> o =
        Observable.just(1, 2)
            .scan(
                0,
                new BiFunction<Integer, Integer, Integer>() {

                  @Override
                  public Integer apply(Integer t1, Integer t2) {
                    return t1 + t2;
                  }
                })
            .take(1);
    TestSubscriber<Integer> subscriber = new TestSubscriber<>();
    o.subscribe(subscriber);
    subscriber.assertValue(0);
    subscriber.assertTerminated();
    subscriber.assertNoErrors();
  }