val testSource = Source(1 until 50)

    val processingFlow: Flow[Int, Int, NotUsed] = Flow[Int].mapAsyncUnordered(10)(x => Future {
      println(s"Kicking off $x")
      Thread.sleep(Random.nextInt(500))
      x * 10
    })

    testSource.via(processingFlow).runWith(Sink.seq[Int])```