[Mockito] 스프링 Mockito 어노테이션 이해하기 - @Mock, @Spy, @InjectMocks, @Captor

단위 테스트를 작성하면서 다시는 헷갈리지 않기 위해 영어 문서(Baeldung)을 참고하여 정리하였습니다.

 

 

@ExtendWith(MockitoExtention.class)

this is specific to JUnit5, and enables Mockito annotations like @Mock, @InjectMocks, and @Spy in the test class

JUnit5에 관한 어노테이션이며, Mockito 어노테이션을 사용할 수 있게 해 줍니다.

@ExtendWith(MockitoExtension.class)
class ExampleTest {

  @InjectMocks
  private ExampleService exampleService;

  @Mock
  ExampleRepository exampleRepository;

  @Test
  void testExample() {
    when(exampleRepository.findById(1))
            .thenReturn(Optional.of(new Example(1)));
    // ...
  }

 

@Mock

The most widely used annotation in Mockito

we can use @Mock to create and inject mocked instances without having to call Mockito.mock manually

해당 어노테이션을 통해 모킹 된 인스턴스를 주입할 수 있습니다.

@Test
public void whenNotUseMockAnnotation_thenCorrect() {
    List mockList = Mockito.mock(ArrayList.class);
    
    mockList.add("one");
    Mockito.verify(mockList).add("one");
    assertEquals(0, mockList.size());

    Mockito.when(mockList.size()).thenReturn(100);
    assertEquals(100, mockList.size());
}

===

@Mock
List<String> mockedList;

@Test
public void whenUseMockAnnotation_thenMockIsInjected() {
    mockedList.add("one");
    Mockito.verify(mockedList).add("one");
    assertEquals(0, mockedList.size());

    Mockito.when(mockedList.size()).thenReturn(100);
    assertEquals(100, mockedList.size());
}

 

@Spy

annotation to spy on an existing instance.

(기존 인스턴스인 척하게 하는 스파이 객체를 만들어줍니다.)

@Spy
List<String> spiedList = new ArrayList<String>();

@Test
public void whenUseSpyAnnotation_thenSpyIsInjectedCorrectly() {
    spiedList.add("one");
    spiedList.add("two");

    Mockito.verify(spiedList).add("one");
    Mockito.verify(spiedList).add("two");

    assertEquals(2, spiedList.size()); //** use real method

    Mockito.doReturn(100).when(spiedList).size();
    assertEquals(100, spiedList.size());
}

• Used the real method spiedList.add() to add elements to the spiedList.
• Stubbed the method spiedList.size() to return 100 instead of 2 using Mockito.doReturn().
  • Mockito.doReturn을 통해 메서드를 스텁 할 수 있습니다.

 

@Captor

annotation to create an ArgumentCaptor instance.

@Test
public void whenNotUseCaptorAnnotation_thenCorrect() {
    List mockList = Mockito.mock(List.class);
    ArgumentCaptor<String> arg = ArgumentCaptor.forClass(String.class);

    mockList.add("one");
    Mockito.verify(mockList).add(arg.capture());

    assertEquals("one", arg.getValue());
}

===

@Mock
List mockedList;

@Captor 
ArgumentCaptor argCaptor;

@Test
public void whenUseCaptorAnnotation_thenTheSame() {
    mockedList.add("one");
    Mockito.verify(mockedList).add(argCaptor.capture());

    assertEquals("one", argCaptor.getValue());
}

@Captor for the same purpose, to create an ArgumentCaptor instance.

 

@InjectMocks

annotation to inject mock fields into the tested object automactically.

테스트 객체에 자동으로 mock 필드를 주입해 주는 어노테이션입니다.

 

https://www.baeldung.com/mockito-annotations