[FIXED] Spring boot @MockMvcTest MockHttpServletResponse always returns empty body

Issue

I'm struggling with a simple spring boot rest controller test which always return empty body response.

Here is my test code looks like:

@WebMvcTest(AdminRestController.class)
@AutoConfigureMockMvc(addFilters = false)
public class PatientsUnitTest {

    @Autowired
    private MockMvc mvc;

    @Autowired
    private ObjectMapper objectMapper;

    @MockBean
    private PatientsService patientsService;

    @MockBean
    private TherapistsService therapistsService;

    @MockBean
    private TherapySchedulesService therapySchedulesService;

    @Test
    public void canAddPatient() throws Exception {
        PatientsSaveRequestDto patientsSaveRequestDto = new PatientsSaveRequestDto();
        patientsSaveRequestDto.setName("Sofia");
        patientsSaveRequestDto.setPhone("01012345678");
        Patients patient = patientsSaveRequestDto.toEntity();

        when(patientsService.createPatient(patientsSaveRequestDto)).thenReturn(patient);

        final ResultActions actions = mvc.perform(post("/admin/patient")
                .contentType(MediaType.APPLICATION_JSON_VALUE)
                .characterEncoding(StandardCharsets.UTF_8.name())
                .content(objectMapper.writeValueAsString(patientsSaveRequestDto)))
                .andDo(print());

        actions
                .andExpect(status().isOk())
                .andExpect(content().contentType(MediaType.APPLICATION_JSON_VALUE))
                .andExpect(jsonPath("name", is(patient.getName())))
                .andDo(print());
    }

My Controller:

@RestController
@RequiredArgsConstructor
public class AdminRestController {
    private final PatientsService patientsService;
    private final TherapistsService therapistsService;
    private final TherapySchedulesService therapySchedulesService;

    @PostMapping("/admin/patient")
    @ResponseStatus(HttpStatus.OK)
    @Operation(summary = "Create a patient")
    public Patients cratePatient(
            @RequestBody @Valid PatientsSaveRequestDto patientsSaveRequestDto
    ) {
        return patientsService.createPatient(patientsSaveRequestDto);
    }

// PatientsService
@Transactional
    public Patients createPatient(PatientsSaveRequestDto patientsSaveRequestDto){
        return patientsRepository.save(patientsSaveRequestDto.toEntity());
    }

And this is the result of print():

MockHttpServletRequest:
      HTTP Method = POST
      Request URI = /admin/patient
       Parameters = {}
          Headers = [Content-Type:"application/json;charset=UTF-8", Content-Length:"53"]
             Body = {"name":"sofia","phone":"01012345678","tel":null}
    Session Attrs = {}

Handler:
             Type = com.ussoft.dosu.web.controller.admin.AdminRestController
           Method = com.ussoft.dosu.web.controller.admin.AdminRestController#cratePatient(PatientsSaveRequestDto)

Async:
    Async started = false
     Async result = null

Resolved Exception:
             Type = null

ModelAndView:
        View name = null
             View = null
            Model = null

FlashMap:
       Attributes = null

MockHttpServletResponse:
           Status = 200
    Error message = null
          Headers = []
     Content type = null
             Body = 
    Forwarded URL = null
   Redirected URL = null
          Cookies = []

As you can see the request is sent correctly but the response values are all null.

When i test the same controller using @SpringBootTest with Rest Assured it works fine.

I'm using Spring boot 2.3.1, Junit5

---

Edit - added PatientsSaveRequestDto

@Getter
@Setter
@NoArgsConstructor
public class PatientsSaveRequestDto {
    @NotBlank(message = "이름은 필수 입력사항입니다.")
    private String name;

    private String phone;

    private String tel;

    public Patients toEntity(){
        return Patients.builder()
                .name(name)
                .phone(phone)
                .tel(tel)
                .build();
    }
}

Solution

You need to provide equals method for PatientsSaveRequestDto.

When you execute a method on a mock, Mockito needs to check if any behaviour was specified for the arguments for which the method was called.

• If the arguments match, the recorded result is returned,
• If the arguments don't match, default value of the method return type is returned (null for all Objects, zero for numerics, false for bools)

You recorded the behaviour with the following call:

when(patientsService.createPatient(patientsSaveRequestDto)).thenReturn(patient);

This means that the actual argument to createPatient will be compared to patientsSaveRequestDto with equals.

Note that this behaviour can be changed by the use of ArgumentMatchers.

The patientsSaveRequestDto from your test and the actual argument to createPatient are not equal because:

• you didn't define the equals method
• they are different instances
• thus, the inherited Object.equals returns false

You have 2 different instances because you created a @WebMvcTest. The patientsSaveRequestDto you send to the controller is first serialized to String and then deserialized, and this is how a second instance got created.

Answered By - Lesiak
Answer Checked By - Pedro (JavaFixing Volunteer)