@Test
public void userCanLogin() {
    String username = "adrianvdh";
    String password = "hello123";
    UserRepository userRepository = new UserRepository();
    UserService userService = new UserService(userRepository);

    User user = userService.authenticate(username, password);

    Assert.assertEquals("adrianvdh", user.username);
    Assert.assertEquals("hello123", user.password);
}