Akka.Streams.Tests.Dsl.FlowGroupBySpec.GroupBy_must_fail_stream_when_GroupBy_function_throws C# (CSharp) Method

        public void GroupBy_must_fail_stream_when_GroupBy_function_throws()
        {
            this.AssertAllStagesStopped(() =>
            {
                var publisherProbe = TestPublisher.CreateManualProbe<int>(this);
                var ex = new TestException("test");
                var publisher = Source.FromPublisher(publisherProbe).GroupBy(2, i =>
                {
                    if (i == 2)
                        throw ex;
                    return i%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.Request(100);

                upstreamSubscription.SendNext(1);

                var substream = subscriber.ExpectNext().Item2;
                var substreamPuppet = new StreamPuppet(substream.RunWith(Sink.AsPublisher<int>(false), Materializer), this);

                substreamPuppet.Request(1);
                substreamPuppet.ExpectNext(1);

                upstreamSubscription.SendNext(2);
                subscriber.ExpectError().Should().Be(ex);
                substreamPuppet.ExpectError(ex);
                upstreamSubscription.ExpectCancellation();
            }, Materializer);
        }