Akka.Streams.Tests.Dsl.FlowConcatAllSpec.ConcatAll_must_pass_along_early_cancellation C# (CSharp) Method

        public void ConcatAll_must_pass_along_early_cancellation()
        {
            this.AssertAllStagesStopped(() =>
            {
                var up = TestPublisher.CreateManualProbe<Source<int, NotUsed>>(this);
                var down = TestSubscriber.CreateManualProbe<int>(this);

                var flowSubscriber = Source.AsSubscriber<Source<int, NotUsed>>()
                    .ConcatMany(x => x.MapMaterializedValue<ISubscriber<Source<int, NotUsed>>>(_ => null))
                    .To(Sink.FromSubscriber(down))
                    .Run(Materializer);

                var downstream = down.ExpectSubscription();
                downstream.Cancel();
                up.Subscribe(flowSubscriber);
                var upSub = up.ExpectSubscription();
                upSub.ExpectCancellation();
            }, Materializer);
        }
    }