Snippet

Mocking Service Dependencies in Spring Unit Tests

Unit testing Spring components requires isolating business logic from external systems like databases. Using Mockito with JUnit 5 enables mocking dependencies via @Mock and automatically injecting them into the target class under test using @InjectMocks.

snippet.java

java

@ExtendWith(MockitoExtension.class)
class UserServiceTest {
 
    @Mock
    private UserRepository userRepository;
 
    @InjectMocks
    private UserService userService;
 
    @Test
    void testFindUserById() {
        when(userRepository.findById(1L)).thenReturn(Optional.of(new User("Alice")));
        User user = userService.getUser(1L);
        assertEquals("Alice", user.getName());
    }
}

spring

Breakdown

@ExtendWith(MockitoExtension.class)

Initializes the Mockito framework for JUnit 5 test lifecycle management.

@Mock private UserRepository userRepository;

Creates a mocked instance of the repository dependency.

@InjectMocks private UserService userService;

Instantiates the UserService and injects the created mocks into it.

when(userRepository.findById(1L)).thenReturn(Optional.of(new User("Alice")));

Stubs the mock repository method to return a predefined User instance when queried with ID 1.

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Mocking Service Dependencies in Spring Unit Tests

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