Mockito 고급: 인수 캡처와 스파이

ArgumentCaptor: 메서드 인수 캡처

ArgumentCaptor 생성 및 사용

@Test
void sends_correct_email() {
    ArgumentCaptor<EmailMessage> captor = ArgumentCaptor.forClass(EmailMessage.class);
    userService.register(new CreateUserRequest("alice@example.com"));
    verify(emailService).send(captor.capture());
    EmailMessage msg = captor.getValue();
    assertEquals("alice@example.com", msg.getTo());
    assertTrue(msg.getSubject().contains("Welcome"));
}

@Captor 어노테이션

@ExtendWith(MockitoExtension.class)
class UserServiceTest {
    @Mock EmailService emailService;
    @Captor ArgumentCaptor<EmailMessage> emailCaptor;
    @Test
    void captures_email() {
        // ...
        verify(emailService).send(emailCaptor.capture());
        assertEquals("Welcome!", emailCaptor.getValue().getSubject());
    }
}

여러 호출 캡처

verify(emailService, times(3)).send(emailCaptor.capture());
List<EmailMessage> messages = emailCaptor.getAllValues();
assertEquals(3, messages.size());
assertEquals("Confirmation", messages.get(0).getSubject());

Mockito 스파이: 부분 모의 처리

List<String> realList = new ArrayList<>();
List<String> spy = Mockito.spy(realList);
spy.add("hello"); // calls real ArrayList.add()
System.out.println(spy.size()); // 1 — real method called
doReturn(42).when(spy).size(); // stub just size()
System.out.println(spy.size()); // 42 — stubbed

@Spy 어노테이션

@ExtendWith(MockitoExtension.class)
class OrderServiceTest {
    @Spy
    OrderService orderService = new OrderService(mockRepo, mockEmail);
}

@SpyBean으로 Spring 빈 감시

@SpringBootTest
class IntegrationTest {
    @SpyBean EmailService emailService;
    @Test
    void order_sends_email() {
        orderService.placeOrder(cart);
        verify(emailService).sendConfirmation(any());
    }
}

스파이에서 doReturn과 when().thenReturn() 비교

// Correct for spies:
doReturn(List.of()).when(spy).findAll();
// WRONG for spies — calls real findAll() first:
when(spy.findAll()).thenReturn(List.of()); // real method called!

상호 작용이 없었는지 검증

verifyNoInteractions(emailService); // never called
verify(repo).save(any());
verifyNoMoreInteractions(repo); // save() was the only interaction

InOrder 검증

InOrder inOrder = inOrder(repo, emailService);
inOrder.verify(repo).save(any());
inOrder.verify(emailService).send(any()); // save happened BEFORE send

인수 매처

verify(repo).save(argThat(user ->
    user.getEmail().endsWith("@example.com") &&
    user.getStatus() == UserStatus.ACTIVE));

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