Mocking iOS Firebase Auth sign-in methods

Question

This question is somewhat similar to Mock third party classes (Firebase) in Swift but different enough to warrant a new question, based on the answers to it.

I'm trying to mock the Auth / FIRAuth method signIn(withEmail email: String, password: String, completion: AuthDataResultCallback?) and am running into difficulties with trying to mock the AuthDataResultCallback object, mainly because it has a User property that I also want to mock. Unfortunately, I'm not able to create my own User or Auth objects because they've been marked as not having an available initializer in Swift.

I have an object (let's call it UserAuthenticationRepository ) that's responsible for performing user authentication and database reads. I'd like to inject a Firebase auth object into it to do these things under the hood, but since I want to test this repository object I'd like to be able to inject a Firebase mock object when I go to unit test it.

What I want to do is something like this (simplified slightly for this question):

import FirebaseAuth

protocol FirebaseUserType {
    var uid: String { get }
}

extension User: FirebaseUserType {}

protocol FirebaseAuthDataResultType {
    var user: FirebaseUserType { get }
}

extension AuthDataResult: FirebaseAuthDataResultType {
    var user: FirebaseUserType {
        // This is where I'm running into problems because AuthDataResult expects a User object, 
        // which I also use in the UserAuthenticationRepository signIn(withEmail:) method
    }
}

protocol FirebaseAuthenticationType {
    func signIn(withEmail email: String, password: String, completion: ((FirebaseAuthDataResultType?, Error?) -> Void)?)
}

extension Auth: FirebaseAuthenticationType {
    func signIn(withEmail email: String, password: String, completion: ((FirebaseAuthDataResultType?, Error?) -> Void)?) {
        let completion = completion as AuthDataResultCallback?
        signIn(withEmail: email, password: password, completion: completion)
    }
}

protocol UserAuthenticationType {
    func loginUser(emailAddress: String, password: String) -> Observable<User>
}

class UserAuthenticationRepository: UserAuthenticationType {
    private let authenticationService: FirebaseAuthenticationType
    private let disposeBag = DisposeBag()

    init(authenticationService: FirebaseAuthenticationType = Auth.auth()) {
        self.authenticationService = authenticationService
    }

    func loginUser(emailAddress: String, password: String) -> Observable<User> {
        return .create { [weak self] observer in
            self?.authenticationService.signIn(withEmail: emailAddress, password: password, completion: { authDataResult, error in
                if let error = error {
                    observer.onError(error)
                } else if let authDataResult = authDataResult {
                    observer.onNext(authDataResult.user)
                }
            })
            return Disposables.create()
        }
    }

As noted above, I'm running into problems when I try to extend AuthDataResult to conform to my FirebaseAuthDataResultType protocol. Is it possible to do what I'm trying to do? I'd ultimately like to pass back a uid string in my Firebase authentication service when testing UserAuthenticationRepository .

Answer 1

I was eventually able to find a way to mock the Firebase Auth objects necessary for me, but I had to resort to subclassing the Firebase User object, adding new properties to it be used during testing (can't create a User object directly or mutate its properties), and then creating a struct which conforms to FirebaseAuthDataResultType which is initialized with a MockUser object during testing. The protocols and extensions I ended up needing are below:

protocol FirebaseAuthDataResultType {
    var user: User { get }
}

extension AuthDataResult: FirebaseAuthDataResultType {}

typealias FirebaseAuthDataResultTypeCallback = (FirebaseAuthDataResultType?, Error?) -> Void

protocol FirebaseAuthenticationType {
    func signIn(withEmail email: String, password: String, completion: FirebaseAuthDataResultTypeCallback?)
    func signOut() throws
    func addStateDidChangeListener(_ listener: @escaping AuthStateDidChangeListenerBlock) -> AuthStateDidChangeListenerHandle
    func removeStateDidChangeListener(_ listenerHandle: AuthStateDidChangeListenerHandle)
}

extension Auth: FirebaseAuthenticationType {
    func signIn(withEmail email: String, password: String, completion: FirebaseAuthDataResultTypeCallback?) {
        let completion = completion as AuthDataResultCallback?
        signIn(withEmail: email, password: password, completion: completion)
    }
}

Below are the mock objects:

class MockUser: User {
    let testingUID: String
    let testingEmail: String?
    let testingDisplayName: String?

    init(testingUID: String,
         testingEmail: String? = nil,
         testingDisplayName: String? = nil) {
        self.testingUID = testingUID
        self.testingEmail = testingEmail
        self.testingDisplayName = testingDisplayName
    }
}

struct MockFirebaseAuthDataResult: FirebaseAuthDataResultType {
    var user: User
}

An instance of my mock Firebase authentication service with stubs:

class MockFirebaseAuthenticationService: FirebaseAuthenticationType {
    typealias AuthDataResultType = (authDataResult: FirebaseAuthDataResultType?, error: Error?)
    var authDataResultFactory: (() -> (AuthDataResultType))?

    func signIn(withEmail email: String, password: String, completion: FirebaseAuthDataResultTypeCallback?) {
      // Mock service logic goes here
    }

    // ...rest of protocol functions
}

Usage (using RxSwift and RxTest ):

func testLoginUserReturnsUserIfSignInSuccessful() {
    let firebaseAuthService = MockFirebaseAuthenticationService()
    let expectedUID = "aM1RyjpaZcQ4EhaUvDAeCnla3HX2"
    firebaseAuthService.authDataResultFactory = {
        let user = MockUser(testingUID: expectedUID)
        let authDataResult = MockFirebaseAuthDataResult(user: user)
        return (authDataResult, nil)
    }

    let sut = UserSessionRepository(authenticationService: firebaseAuthService)
    let userObserver = testScheduler.createObserver(User.self)

    sut.loginUser(emailAddress: "john@gmail.com", password: "123456")
       .bind(to: userObserver)
       .disposed(by: disposeBag)

    testScheduler.start()

    let user = userObserver.events[0].value.element as? MockUser

    // Assert MockUser properties, events, etc.
}

If anyone has any better ideas of how this can be accomplished, please let me know!