Tauri-demo: refactor login and signup mocks

auth.spec.ts

function setUserCreds(firebaseAuth: any, successful: boolean, user = {
    uid: '123',
    email: 'test@test.com'
}) {
    return async () => {
        (firebaseAuth.getAuth as any).mockReturnValue({
            currentUser: successful ? user : null
        });

        if (successful) firebaseAuth.authChangeCallback();

        return {
            user
        };
    }
}

function setLogin(firebaseAuth: any, successful: boolean) {
    (firebaseAuth.signInWithEmailAndPassword as any).mockImplementation(setUserCreds(firebaseAuth, successful));
}

function setSignUp(firebaseAuth: any, successful: boolean) {
    (firebaseAuth.createUserWithEmailAndPassword as any).mockImplementation(setUserCreds(firebaseAuth, successful));
}