Test Double

class DummyUser implements User {
    @Override
    public String getUsername() {
        return null; // 아무 동작도 하지 않음
    }
}

// 테스트 코드
@Test
void testDummy() {
    NotificationService notificationService = new NotificationService();
    notificationService.sendNotification(new DummyUser()); // 실제 사용 X
}

class PaymentServiceStub implements PaymentService {
    @Override
    public boolean processPayment(double amount) {
        return true; // 항상 성공 반환
    }
}

// 테스트 코드
@Test
void testStub() {
    PaymentServiceStub paymentStub = new PaymentServiceStub();
    OrderService orderService = new OrderService(paymentStub);

    assertTrue(orderService.placeOrder(100.0)); // 항상 성공
}

class FakeUserRepository implements UserRepository {
    private Map<String, User> database = new HashMap<>();

    @Override
    public void save(User user) {
        database.put(user.getUsername(), user);
    }

    @Override
    public User findByUsername(String username) {
        return database.get(username);
    }
}

// 테스트 코드
@Test
void testFake() {
    FakeUserRepository fakeRepo = new FakeUserRepository();
    User user = new User("testUser");
    fakeRepo.save(user);

    assertEquals(user, fakeRepo.findByUsername("testUser")); // 저장된 객체 반환
}

class SpyList<T> extends ArrayList<T> {
    private int addCallCount = 0;

    @Override
    public boolean add(T element) {
        addCallCount++;
        return super.add(element);
    }

    public int getAddCallCount() {
        return addCallCount;
    }
}

// 테스트 코드
@Test
void testSpy() {
    SpyList<String> spyList = new SpyList<>();

    spyList.add("hello");
    spyList.add("world");

    assertEquals(2, spyList.getAddCallCount()); // add()가 몇 번 호출되었는지 검증
}

@ExtendWith(MockitoExtension.class)
public class UserServiceTest {

    @Mock
    private UserRepository userRepository;

    @InjectMocks
    private UserService userService;

    @Test
    public void shouldReturnUserWhenUserIdIsProvided() {
        // Given
        Long userId = 1L;
        User mockUser = new User(userId, "John Doe", "john@example.com");
        when(userRepository.findById(userId)).thenReturn(mockUser);

        // When
        User result = userService.getUserById(userId);

        // Then
        assertNotNull(result);
        assertEquals("John Doe", result.getName());
        verify(userRepository).findById(userId);
    }
    
    @Test
    public void shouldThrowExceptionWhenUserNotFound() {
        // Given
        Long userId = 2L;
        when(userRepository.findById(userId)).thenThrow(new UserNotFoundException("User not found"));

        // When & Then
        assertThrows(UserNotFoundException.class, () -> userService.getUserById(userId));
        verify(userRepository).findById(userId);
    }
}

when(userRepository.findById(userId)).thenReturn(mockUser);

assertNotNull(result);
assertEquals("John Doe", result.getName());

verify(userRepository).findById(userId);