Subclassing RxSwift/Reactive extension for stubbing

Question

Say I have a Field class with a harvest function like this:

class Field {

    func harvest(handler: (Vegetable) -> Void) {
        …
        handler(carrot)
        …
        handler(potato)
        …
        handler(carrot)
        …
    }
}

I also have a Reactive version/API for the same function:

import RxSwift

extension Reactive where Base: Field {

    func harvest() -> Observable<Vegetable> {
        return Observable.create { observer in
            self.base.harvest(handler: observer.onNext)

            return Disposables.create()
        }
    }
}

For testing purposes, I created a subclass of Field named MockField that overrides harvest(:) to invoke the handler with a set of stubbed Vegetable s. When using the MockField object like field.harvest(:) everything works fine and I get the stubbed vegetables.

Now I want to do the same with the Reactive extension to stub calls to field.rx.harvest , but I cannot override it to return stubbed Vegetables! How can I override functions in the rx namespace?

Answer 1

Probably the easiest way to do this would not be subclassing, but defining harvest() -> Observable<Vegetable> in terms of Field.harvest(handler:)

import RxSwift

extension Reactive where Base: Field {

    func harvest() -> Observable<Vegetable> {
        return Observable.create { observer in
            self.base.harvest(handler: observer.onNext)

            return Disposables.create()
        }
    }
}

Doing it this way you will not need to maintain two implementations of harvest .

PS: The block passed to a disposable should cancel the action, not send the completed event. If there is no facility to cancel harvest(handler:) , you can simply return Disposables.create() .