How to write unit tests for Spring Boot controllers with WebMvcTest?

Question

I want to write unit tests for my REST controllers in Spring Boot. I've heard about @WebMvcTest but I'm not sure how to use it properly.

How do I:
1. Test controller methods in isolation
2. Mock service layer dependencies
3. Test request/response validation
4. Verify security filters

Here's my controller:
```java
@RestController
@RequestMapping("/api/users")
public class UserController {
    @Autowired
    private UserService userService;

@GetMapping("/{id}")
    public User getUser(@PathVariable Long id) {
        return userService.findById(id);
    }
}
```

boot_dev · Accepted Answer

Here's how to properly test Spring Boot controllers with @WebMvcTest:

**Controller Test:**
```java
@WebMvcTest(UserController.class)
@AutoConfigureMockMvc(addFilters = false)  // Skip security filters for unit tests
class UserControllerTest {

@Autowired
    private MockMvc mockMvc;

@MockBean
    private UserService userService;

@Autowired
    private ObjectMapper objectMapper;

@Test
    void getUser_Success() throws Exception {
        // Given
        User user = User.builder()
            .id(1L)
            .name("John Doe")
            .email("john@example.com")
            .build();

when(userService.findById(1L)).thenReturn(user);

// When & Then
        mockMvc.perform(get("/api/users/1")
                .contentType(MediaType.APPLICATION_JSON))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.id").value(1))
            .andExpect(jsonPath("$.name").value("John Doe"))
            .andExpect(jsonPath("$.email").value("john@example.com"));

verify(userService).findById(1L);
    }

@Test
    void createUser_ValidationError() throws Exception {
        // Given - invalid user (empty name)
        UserDTO userDTO = new UserDTO();
        userDTO.setEmail("invalid");

// When & Then
        mockMvc.perform(post("/api/users")
                .contentType(MediaType.APPLICATION_JSON)
                .content(objectMapper.writeValueAsString(userDTO)))
            .andExpect(status().isBadRequest())
            .andExpect(jsonPath("$.errors.name").exists());
    }
}
```

**Integration Test (with database):**
```java
@SpringBootTest
@AutoConfigureMockMvc
@Transactional
class UserControllerIntegrationTest {

@Autowired
    private MockMvc mockMvc;

@Autowired
    private UserRepository userRepository;

@Test
    void getUser_Integration() throws Exception {
        // Setup real data
        User user = userRepository.save(new User("John", "john@test.com"));

mockMvc.perform(get("/api/users/" + user.getId()))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.name").value("John"));
    }
}
```

**Key Points:**
- @WebMvcTest loads only web layer components
- Use @MockBean to mock service layer
- MockMvc simulates HTTP requests without server
- ObjectMapper for JSON serialization

1 Answer