Adrianvdh

public class AuthorisationContext {

    public void authenticate(String username, String password) {

    }
}

Adrianvdh

public class UserRepositoryImpl implements UserRepository {

    @Override
    public User findByUsername(String username) {
        return new User();
    }
}

Adrianvdh

public interface UserRepository {
    User findByUsername(String username);
}

Adrianvdh

@Test(expected = RuntimeException.class)
public void userLoginWhereUserIsNotFound() {
    String username = "kentbeck";
    String password = "letmein";
    UserRepository userRepository = new UserRepositoryImpl();
    UserService userService = new UserService(userRepository);

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

Adrianvdh

public class UserService {

    private UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User authenticate(String username, String password) {
        User foundUser = userRepository.findByUsername(username)

Adrianvdh

public class UserService {

    private UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User authenticate(String username, String password) {
        User foundUser = null;

Adrianvdh

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

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

    Assert.assertEquals("adrianvdh", user.username);

Adrianvdh

@Test(expected = RuntimeException.class)
public void testFindByUsername_UsernameNotFound() {
    String username = "kentb";
    UserRepository userRepository = new UserRepositoryImpl();

    //when
    User user = userRepository.findByUsername(username);
}

Adrianvdh

public class UserRepositoryImpl implements UserRepository {

    Set<User> users = new HashSet<>();

    {
        User user = new User();
        user.username = "adrianvdh";
        user.password = "hello123";
        users.add(user);
    }

Adrianvdh

@Test
public void testFindByUsername() {
    String username = "adrianvdh";
    UserRepository userRepository = new UserRepositoryImpl();

    User user = userRepository.findByUsername(username);

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