java-spring-mockito-mock-mockbean
Mockito.mock() vs @Mock vs @MockBean
Further reading:
Mockito ArgumentMatchers
Learn how to use the ArgumentMatcher and how it differs from the ArgumentCaptor.
Mocking Exception Throwing using Mockito
Learn to configure a method call to throw an exception in Mockito.
2. Mockito.mock()
Then, we can use the mock to stub return values for its methods and verify if they were called.
Let’s look at an example:
@Test
public void givenCountMethodMocked_WhenCountInvoked_ThenMockedValueReturned() {
UserRepository localMockRepository = Mockito.mock(UserRepository.class);
Mockito.when(localMockRepository.count()).thenReturn(111L);
long userCount = localMockRepository.count();
Assert.assertEquals(111L, userCount);
Mockito.verify(localMockRepository).count();
}This method doesn’t need anything else to be done before it can be used. We can use it to create mock class fields as well as local mocks in a method.
3. Mockito’s @Mock Annotation
This annotation is a shorthand for the Mockito.mock() method. As well, we should only use it in a test class. Unlike the mock() method, we need to enable Mockito annotations to use this annotation.
We can do this either by using the MockitoJUnitRunner to run the test or calling the MockitoAnnotations.initMocks() method explicitly.
Let’s look at an example using MockitoJUnitRunner:
@RunWith(MockitoJUnitRunner.class)
public class MockAnnotationUnitTest {
@Mock
UserRepository mockRepository;
@Test
public void givenCountMethodMocked_WhenCountInvoked_ThenMockValueReturned() {
Mockito.when(mockRepository.count()).thenReturn(123L);
long userCount = mockRepository.count();
Assert.assertEquals(123L, userCount);
Mockito.verify(mockRepository).count();
}
}Apart from making the code more readable, @Mock makes it easier to find the problem mock in case of a failure, as the name of the field appears in the failure message:
Wanted but not invoked:
mockRepository.count();
-> at org.baeldung.MockAnnotationTest.testMockAnnotation(MockAnnotationTest.java:22)
Actually, there were zero interactions with this mock.
at org.baeldung.MockAnnotationTest.testMockAnnotation(MockAnnotationTest.java:22)Also, when used in conjunction with @InjectMocks, it can reduce the amount of setup code significantly.
4. Spring Boot’s @MockBean Annotation
We can use the @MockBean to add mock objects to the Spring application context. The mock will replace any existing bean of the same type in the application context.
If no bean of the same type is defined, a new one will be added. This annotation is useful in integration tests where a particular bean – for example, an external service – needs to be mocked.
To use this annotation, we have to use SpringRunner to run the test:
@RunWith(SpringRunner.class)
public class MockBeanAnnotationIntegrationTest {
@MockBean
UserRepository mockRepository;
@Autowired
ApplicationContext context;
@Test
public void givenCountMethodMocked_WhenCountInvoked_ThenMockValueReturned() {
Mockito.when(mockRepository.count()).thenReturn(123L);
UserRepository userRepoFromContext = context.getBean(UserRepository.class);
long userCount = userRepoFromContext.count();
Assert.assertEquals(123L, userCount);
Mockito.verify(mockRepository).count();
}
}When we use the annotation on a field, as well as being registered in the application context, the mock will also be injected into the field.
This is evident in the code above. Here, we have used the injected UserRepository mock to stub the count method_._ We have then used the bean from the application context to verify that it is indeed the mocked bean.
5. Conclusion
In this article, we saw how the three methods for creating mock objects differ and how each can be used.
The source code that accompanies this article is available over on GitHub.
