public void GroupBy_must_accept_cancellation_of_master_stream_when_not_consume_anything()
{
this.AssertAllStagesStopped(() =>
{
var publisherProbe = TestPublisher.CreateManualProbe<int>(this);
var publisher =
Source.FromPublisher(publisherProbe)
.GroupBy(2, x => x%2)
.Lift(x => x%2)
.RunWith(Sink.AsPublisher<Tuple<int, Source<int, NotUsed>>>(false), Materializer);
var subscriber = TestSubscriber.CreateManualProbe<Tuple<int, Source<int, NotUsed>>>(this);
publisher.Subscribe(subscriber);
var upstreamSubscription = publisherProbe.ExpectSubscription();
var downstreamSubscription = subscriber.ExpectSubscription();
downstreamSubscription.Cancel();
upstreamSubscription.ExpectCancellation();
}, Materializer);
}