How to test a private function inside an RxSwift observer?

Question

observable.subscribe(onNext: { _ in
    somePrivateFunction()
})

What is the RxSwift way to test that when observable receives an event the somePrivateFunction actually gets called or not? Since the subscription and the function are in the same class I can't mock it.

Answer 1

You need to check if any logic is placed in a subscription that can block call of this function. If there is - it may be worth to extract it to a parameter (eg. filter) so that logic can be a part of stream itself.

I assume that observable (source) is injected/redirected from another component (if it's not, most probably it should be). To mock that signal you can use TestableObservable, you can read more here: http://adamborek.com/rxtests-rxactionsheet/

Last but not least - you need to identify what kind of action somePrivateFunction() does. If it's setting some external values - then you can test that outgoing connection from that function. If it sets some internal flags - you can test if value of that flag has changed.