Mockito: 목 객체와 스텁

import org.junit.jupiter.api.*;
import org.mockito.*;
import org.mockito.junit.jupiter.MockitoExtension;
import static org.junit.jupiter.api.Assertions.*;
import static org.mockito.Mockito.*;

@ExtendWith(MockitoExtension.class)
class UserServiceTest {

    @Mock UserRepository userRepo;
    @Mock PasswordEncoder encoder;
    @InjectMocks UserService userService;

    @Test
    void signup_success() {
        // given
        when(userRepo.existsByEmail("alice@example.com")).thenReturn(false);
        when(encoder.encode("pass")).thenReturn("hashed");
        when(userRepo.save(any(User.class)))
            .thenAnswer(inv -> inv.getArgument(0));

        // when
        User user = userService.signup(new SignupDto("alice@example.com", "pass", "Alice"));

        // then
        assertEquals("alice@example.com", user.getEmail());
        assertEquals("hashed", user.getPassword());

        // verify — 호출 검증
        verify(userRepo).existsByEmail("alice@example.com");
        verify(encoder).encode("pass");
        verify(userRepo).save(any(User.class));
        verifyNoMoreInteractions(userRepo, encoder);
    }
}

@Test
void signup_captures_user() {
    when(userRepo.save(any(User.class))).thenAnswer(inv -> inv.getArgument(0));

    userService.signup(new SignupDto("alice@example.com", "pass", "Alice"));

    ArgumentCaptor<User> captor = ArgumentCaptor.forClass(User.class);
    verify(userRepo).save(captor.capture());

    User saved = captor.getValue();
    assertEquals("alice@example.com", saved.getEmail());
    assertEquals("hashed", saved.getPassword());
}

@Test
void findById_not_found() {
    when(userRepo.findById(999L)).thenReturn(Optional.empty());

    assertThrows(UserNotFoundException.class,
        () -> userService.findById(999L));

    // 호출 횟수 검증
    verify(userRepo, times(1)).findById(999L);
    verify(userRepo, never()).save(any());
}


@Test
void external_api_throws() {
    when(externalApi.call())
        .thenThrow(new IOException("Network error"));

    assertThrows(ServiceUnavailableException.class,
        () -> service.callExternal());
}

@Test
void retry_logic() {
    when(api.call())
        .thenThrow(new IOException("first fail"))
        .thenThrow(new IOException("second fail"))
        .thenReturn("success");

    String result = retryService.callWithRetry();
    assertEquals("success", result);
    verify(api, times(3)).call();
}


// 인자별 다른 결과
when(repo.findByEmail("alice@example.com")).thenReturn(Optional.of(user1));
when(repo.findByEmail("bob@example.com")).thenReturn(Optional.of(user2));
when(repo.findByEmail(anyString())).thenReturn(Optional.empty());  // default

@Test
void spy_partial_mock() {
    UserService spy = spy(new UserService(userRepo, encoder));

    // 일부 메서드만 stub
    doReturn(true).when(spy).isPremium(any(User.class));

    // 나머지는 실제 동작
    User result = spy.findById(1L);  // 실제 findById 동작
    assertTrue(spy.isPremium(result));  // stub 동작
}