Mocking a class with Rx extensions - ios

Question

Im trying to achieve dependency injection with protocols in Swift :)
My system under test calls .rx.signIn() on the dependency, meaning that it has extended Reactive where Base : ConcreteObject.
Is it possible to setup a protocol ready to receive .rx calls?
Any small example or alternative would be greatly appreciated.

Answer 1

I had the same problem during the upgrade from RxSwift2 to RxSwift3. In RxSwift2 I simply used a protocol for the rx-methods in my production code (ex. rx_JSON()) and injected a simple mock object adhering to that protocol in my unit tests.
After a short detour into generics, associated type and type erasure I settled with the following setup, which closely matches my RxSwift2-setup:
For example to hide URLSession as the concrete implementation of my HTTP-calls, I created a protocol RemoteClient:
protocol RemoteClient {
func json(url: URL) -> Observable<Any>
}
Then in my production code I reference only that protocol:
class SomeService {
var remoteClient: RemoteClient
init(remoteClient: RemoteClient) {
self.remoteClient = remoteClient
}
func getSomeData(_ id: String) -> Observable<JSONDictionary> {
let urlString = "..."
return remoteClient
.json(url: URL(string: urlString)!)
.map { data in
guard let show = data as? JSONDictionary else {
throw ParsingError.json
}
return show
}
}
}
In my unit tests I created mock objects which adhere to the RemoteClient protocol:
class RemoteClientMock: RemoteClient {
var output: Any?
var verifyInput: ((URL) -> Void)?
func json(url: URL) -> Observable<Any> {
verifyInput?(url)
return Observable.create { observer in
if let data = self.output {
observer.on(.next(data))
}
observer.on(.completed)
return Disposables.create()
}
}
}
And inject them in the system under test:
class SomeServiceTest: TestCase {
let disposeBag = DisposeBag()
func testGetSomeData() {
// setup
let expectation = self.expectation(description: "request succeeded")
let remoteClientMock = RemoteClientMock()
remoteClientMock.verifyInput = { url in
XCTAssertEqual(URL(string: "some url"), url)
}
remoteClientMock.output = ["id": 4711]
let service = SomeService(remoteClient: remoteClientMock)
// exercise
let observable = service.getSomeData("4711")
// verify
observable
.subscribe(onNext: { data in
XCTAssertEqual(4711, data["id"] as? Int)
expectation.fulfill()
})
.addDisposableTo(disposeBag)
waitForExpectations(timeout: 1, handler: nil)
}
}
So I simply hide the rx-namespace behind my protocol. I do that for now by using an adapter:
let remoteClient = URLSessionRemoteClientAdapter(urlSession: URLSession.shared)
let service = SomeService(remoteClient: remoteClient)
struct URLSessionRemoteClientAdapter: RemoteClient {
let urlSession: URLSession
init(urlSession: URLSession) {
self.urlSession = urlSession
}
func json(url: URL) -> Observable<Any> {
return urlSession.rx.json(url: url)
}
}