timeout.scala

val sumConsumer: Consumer[Int,Long] =
      new Consumer[Int,Long] {
        def createSubscriber(cb: Callback[Long], s: Scheduler) = {
          val out = new Subscriber.Sync[Int] {
            implicit val scheduler = s
            private var sum = 0L

            def onNext(elem: Int): Continue = {
              sum += elem
              Thread.sleep(20000)
              Continue
            }

            def onComplete(): Unit = {
              // We are done so we can signal the final result
              cb.onSuccess(sum)
            }

            def onError(ex: Throwable): Unit = {
              // Error happened, so we signal the error
              cb.onError(ex)
            }
          }

          // Returning a tuple of our subscriber and a dummy
          // AssignableCancelable because we don't indent to use it
          (out, AssignableCancelable.dummy)
        }
      }

    val source = Observable.interval(1 second)

    val task = source.take(5)
      .map(x => 1)
      .timeoutOnSlowDownstream(1 second)
      .runWith(sumConsumer)

    Await.ready(task.runAsync, 10 seconds).value.get match {
      case Failure(ex: DownstreamTimeoutException) => fail("Yay, got timeout!")
      case Failure(e) => fail("Wrong exception type: " + e)
      case Success(v) => fail("Expected a timeout exception, got: " + v)
    }