public void Error_First_Source() { var us1 = new MonocastSubject <int>(); var us2 = new MonocastSubject <int>(); var to = ObservableSource.Zip(a => { int s = 0; foreach (var v in a) { s += v; } return(s); }, us1.Hide(), us2.Hide() ).Test(); us2.OnNext(1); to.AssertEmpty(); us2.OnNext(2); to.AssertEmpty(); us1.OnNext(10); to.AssertValuesOnly(11); us1.OnError(new InvalidOperationException()); Assert.False(us2.HasObserver()); to.AssertFailure(typeof(InvalidOperationException), 11); }