public void Contains_ArgumentChecking()
{
ReactiveAssert.Throws <ArgumentNullException>(() => Observable.Contains(default(IObservable <int>), 42));
ReactiveAssert.Throws <ArgumentNullException>(() => Observable.Contains(default(IObservable <int>), 42, EqualityComparer <int> .Default));
ReactiveAssert.Throws <ArgumentNullException>(() => Observable.Contains(DummyObservable <int> .Instance, 42, null));
}