Need to mock Firebase Auth but unsure how

Question

I use Firebase to manage authentication within my app. This has a singleton object for the logged in user: Auth.auth().currentUser

In part of my code I check that the uid of the logged in user is equal to a userId associated with an object.

I need to test code that uses this check. For this I need to be able to inject a mock Firebase Auth object.

How can I mock the Firebase Auth object? Has anyone had experience with this before?

Answer 1

So I solved this by creating a few protocols for authentication and making User conform to that protocol:

protocol AuthUser {
    var uid: String {get}
    var displayName: String? {get}
    var email: String? {get}
    var photoURL: URL? {get}
}

extension User : AuthUser {}

protocol AuthenticationProtocol {
    var currentUser: AuthUser? {get}
}

Then I created an Authentication class that conforms to the AuthenticationProtocol:

final class Authentication: AuthenticationProtocol {
    static let shared = Authentication()
    private let auth = Auth.auth()
    var currentUser: AuthUser? {
        return auth.currentUser
}

When I have a class that needs authentication in my app I inject a class that conforms to AuthenticationProtocol like this:

final class MyClass {
    private let auth: AuthenticationProtocol

    init(auth: AuthenticationProtocol = Authentication.shared) {
        self.auth = auth
}

Then I can get the id of the current logged in user by calling auth.currentUser?.uid.

For tests I then create a mock class that conforms to AuthenticationProtocol like this:

final class AuthenticationMock : AuthenticationProtocol {
    private let uid: String
    let currentUser: AuthUser?

    init(currentUser: AuthUser) {
        self.currentUser = currentUser
    }
}

And then I can inject that when I call MyClass(auth: <Authentication Mock Instance>)