Short description of the issue:

I know there is already an issue, #1480, discussing this case, and @abdulowork had replied the reason and gave an alternative way to test PublishSubject.

But I don't think the limitation is reasonable since when we test some mechanism using Observable, we not know if this observable is derived from PublishSubject or not.

Moreover, it's possible that developers may change underlying implementation from ReplaySubject to PublishSubject for some reason, and then related test cases failed

Thus, I suggest to fix the behavior of for Observable.toBlocking(). Here is the possible implementation:

private var disposeBag: DisposeBag!
extension ObservableConvertibleType {
    public func toBlocking(timeout: TimeInterval? = nil) -> BlockingObservable<Element> {
         let replaySubject = ReplaySubject<Element>.createUnbounded()

         // forward all events to replaySubject
         asObservable().subscribe(replaySubject)
             .disposed(by: disposeBag)

         return BlockingObservable(timeout: timeout, source: replaySubject)
    }
}