  @Test
  public void fixed() {

    final AtomicInteger count = new AtomicInteger(0);
    final TestScheduler scheduler = new TestScheduler();
    final RxBackoff backoff = new RxBackoff(
        new Backoff.Builder()
            .setAlgorithm(new FixedIntervalAlgorithm())
            .setMaxRetryCount(5)
            .build(),
        scheduler);
    final TestObserver observer = Observable
        .fromCallable(new Callable<Integer>() {
          @Override public Integer call() throws Exception {
            throw new Exception("error " + count.incrementAndGet());
          }
        })
        .retryWhen(backoff.observable())
        .subscribeOn(scheduler)
        .test();

    scheduler.advanceTimeTo(90_0000L, TimeUnit.MILLISECONDS);
    scheduler.triggerActions();
    observer.awaitTerminalEvent(1000L, TimeUnit.MILLISECONDS);
    observer.assertError(Exception.class);
    assertThat(count.get()).isEqualTo(6); // try(1 time) + retry(5 times)
  }