@MockBean Not Working with @WebMvcTest in Spring Boot 2: A Troubleshooting Guide
Problem: You're using Spring Boot 2 with JUnit 5 and @WebMvcTest for testing your controller. You're using @MockBean to mock dependencies, but the mocks aren't working as expected.
Solution: This is a common problem that arises from the way Spring Boot handles dependency injection within the @WebMvcTest context. Let's dive into the issue and see how to fix it.
Scenario:
Imagine you have a controller, UserController, that relies on a UserService to fetch user data:
@RestController
public class UserController {
private final UserService userService;
@Autowired
public UserController(UserService userService) {
this.userService = userService;
}
@GetMapping("/users/{id}")
public User getUser(@PathVariable Long id) {
return userService.getUserById(id);
}
}
You want to test this controller using @WebMvcTest, and mock the UserService to control the returned data. This is where @MockBean comes in:
@WebMvcTest(UserController.class)
class UserControllerTest {
@MockBean
private UserService userService;
@Autowired
private MockMvc mockMvc;
@Test
void testGetUser() throws Exception {
// Setup mocked behavior for userService
when(userService.getUserById(anyLong())).thenReturn(new User(1L, "Test User"));
mockMvc.perform(get("/users/1"))
.andExpect(status().isOk())
.andExpect(content().json("{\"id\": 1, \"name\": \"Test User\"}"));
}
}
However, you might encounter the issue where the mocked UserService isn't being used in the test, and instead, the real UserService is being injected, causing the test to fail.
Explanation:
The problem arises because @WebMvcTest focuses on testing your controllers and the web layer. It doesn't include the entire application context, which means it might not include your UserService implementation unless it's directly related to the web layer.
Solution:
There are two main ways to address this:
-
Explicitly Import
UserService: You can importUserServicein your@WebMvcTestannotation using theimportattribute:@WebMvcTest(controllers = UserController.class, import = UserService.class) class UserControllerTest { // ... }This ensures that Spring Boot includes
UserServicein the@WebMvcTestcontext and allows@MockBeanto work correctly. -
Use
@SpringBootTest: If you need to mock dependencies outside the web layer, it's better to use@SpringBootTestinstead of@WebMvcTest.@SpringBootTeststarts the full Spring context, allowing you to mock any dependency, including services likeUserService. However, be mindful that@SpringBootTestmight be slower and require more setup.
Additional Tips:
- Clear the Cache: If you're still experiencing issues, clear your application cache (target folder) before running your tests.
- Verify the Mock: Double-check the mocking behavior of your
@MockBeanby using a debugging tool or adding assertions to confirm that the mock is being invoked. - Consult the Documentation: The Spring Boot documentation provides detailed information on testing and dependency injection. https://docs.spring.io/spring-boot/docs/current/reference/html/spring-boot-features.html#boot-features-testing
Example:
Here's an example of how to use the import attribute with @WebMvcTest:
@WebMvcTest(controllers = UserController.class, import = UserService.class)
class UserControllerTest {
@MockBean
private UserService userService;
// ... your test code
}
By understanding the nuances of Spring Boot's dependency injection and @WebMvcTest, you can effectively mock dependencies and ensure robust testing of your controllers. Remember to choose the most appropriate testing approach based on your needs and the complexity of your application.
