How to mock beans Autowired on service layer in #WebMvcTest - spring-boot

Question

I am testing a REST API's in Spring boot gradle app, my mocked service using #MockBean is returning null. This mocked service return null if there are some beans Autowired in service class(I used constructor injection).
Here is sample Code(Not compiled, only for understanding)
#RestController
#RequestMapping("/xxx")
class TestController {
private RetriveDataService retriveDataService;
public TestControllerx(RetriveDataService retriveDataService) {
this.retriveDataService = retriveDataService;
}
#PostMapping(value = "/yyy")
public MyResponseModel myMethod(#RequestBody MyRequestModel model) {
return retriveDataService.retriveData(model);
}
}
#Service
class RetriveDataService {
private TokenService tokenService;
public RetriveDataService(TokenService tokenService) {
this.tokenService = tokenService;
}
public MyResponseModel retriveData(MyRequestModel model) {
String accessToken = tokenService.getToken().getAccessToken();
return retriveData(model, accessToken);
}
}
#RunWith(SpringRunner.class)
#WebMvcTest(TestController.class)
public class TestControllerTest {
#Autowired
private MockMvc mvc;
#Autowired
private ObjectMapper objectMapper;
#MockBean
private RetriveDataService retriveDataService;
#Test
public void testRetriveData() throws Exception {
mvc.perform(MockMvcRequestBuilders.post("/xxx/yyy").content(objectMapper.writeValueAsString(new MyRequestModel()))
.contentType(MediaType.APPLICATION_JSON_UTF8)).andDo(MockMvcResultHandlers.print())
.andExpect(content().contentType(MediaType.APPLICATION_JSON_UTF8));
}
}
When I run this test, i am getting following output(If my service do not need another bean, I am getting expected output)
MockHttpServletResponse:
Status = 200
Error message = null
Headers = []
Content type = null
Body =
Forwarded URL = null
Redirected URL = null
Cookies = []
Due to this response i facing problem on line .andExpect(content().contentType(MediaType.APPLICATION_JSON_UTF8));. also when i check response body(as body is also a null)
Sample project to reproduce the issue is here

Answer 1

Checking your repository confirmed assumption form the discussion in comments under question.
You specify expectations on your mock
MyModel requestMessage = new MyModel();
requestMessage.setMessage("Hello Request Post");
given(testService1.getMessage(requestMessage)).willReturn(responseMessage);
but the message received to in your controller in your #WebMvcTest is not equal to requestMessage specified in the test. This is due to the fact that MyModel class does not override equals method.
In this situation, Mockito will use its default behaviour:
By default, for all methods that return a value, a mock will return either null, a primitive/primitive wrapper value, or an empty collection, as appropriate. For example 0 for an int/Integer and false for a boolean/Boolean.
You have two options to fix the problem:
override equals (and hashCode) in your request class.
Get acquainted with argument matchers
More info on option 2.:
Technically, your expectation is equivalent to:
given(testService1.getMessage(ArgumentMatchers.eq(requestMessage)))
.willReturn(responseMessage);
You can use other matcher, or even define your own. This is useful if you cannot modify code of your argument's type (type coming from 3-rd party library etc).
For example, you can use ArgumentMatchers.any(MyModel.class))