How to check values in response body with mockMvc - AssertionError: Status expected:<201> but was:<400>

Question

im new to test writing and i am trying to write junit tests for my controller class using mockMvc.

Here are my classes:

public class StudentDTO {

private final String firstName;
private final String lastName;
private final String JMBAG;
private final Integer numberOfECTS;
private final boolean tuitionShouldBePaid;}

Command class

public class StudentCommand { 
@NotBlank (message = "First name must not be empty!")
private String firstName;

@NotBlank (message = "Last name must not be empty!")
private String lastName;


@NotNull(message = "Date of birth must be entered!")
@Past(message = "Date of birth must be in the past!")
private LocalDate dateOfBirth;

@NotBlank(message = "JMBAG must not be empty!")
@Pattern(message = "JMBAG must have 10 digits", regexp = "[\\d]{10}")
private String jmbag;

@NotNull(message = "Number of ECTS points must be entered!")
@PositiveOrZero(message = "Number of ECTS points must be entered as a positive integer!")
private Integer numberOfECTS;}

Controller class:

@Secured({"ROLE_ADMIN"})
@PostMapping
public ResponseEntity<StudentDTO> save(@Valid @RequestBody final StudentCommand command){
    return studentService.save(command)
            .map(
                    studentDTO -> ResponseEntity
                            .status(HttpStatus.CREATED)
                            .body(studentDTO)
            )
            .orElseGet(
                    () -> ResponseEntity
                            .status(HttpStatus.CONFLICT)
                            .build()
            );
}

Test class:

@SpringBootTest
@AutoConfigureMockMvc class StudentControllerTest {
@Autowired
private MockMvc mockMvc;

@MockBean
private StudentService studentServiceMock;

@Autowired
private ObjectMapper objectMapper;

private final String TEST_FIRST_NAME = "Marry";
private final String TEST_LAST_NAME = "Blinks";
private final String TEST_JMBAG = "0025478451";
private final Integer TEST_NUMBER_OF_ECTS = 55;
private final boolean TEST_TUITION_SHOULD_BE_PAID = true;
private final LocalDate TEST_DATE_OF_BIRTH = LocalDate.parse("1999-01-12");

@Test
void testSave() throws Exception {

    StudentCommand studentCommand = new StudentCommand(TEST_FIRST_NAME,TEST_LAST_NAME,TEST_DATE_OF_BIRTH,TEST_JMBAG,TEST_NUMBER_OF_ECTS);

    this.mockMvc.perform(
            post("/student")
                    .with(user("admin")
                            .password("test")
                            .roles("ADMIN")
                    )
                    .with(csrf())
            .contentType(MediaType.APPLICATION_JSON)
            .content(objectMapper.writeValueAsString(studentCommand))
            .accept(MediaType.APPLICATION_JSON)
    )
            .andExpect(status().isCreated())
            .andExpect(content().contentType(MediaType.APPLICATION_JSON))
            .andExpect(jsonPath("$.jmbag").value(TEST_JMBAG))
            .andExpect(jsonPath("$.firstName").value(TEST_FIRST_NAME))
            .andExpect(jsonPath("$.lastName").value(TEST_LAST_NAME));
}

I always get test failed with this error:

MockHttpServletRequest:
      HTTP Method = POST
      Request URI = /student
       Parameters = {_csrf=[30de7a8f-a3d5-429d-a778-beabd1a533da]}
          Headers = [Content-Type:"application/json;charset=UTF-8", Accept:"application/json", Content-Length:"272"]
             Body = {"firstName":"Marry","lastName":"Blinks","dateOfBirth":{"year":1999,"month":"JANUARY","monthValue":1,"dayOfMonth":12,"chronology":{"id":"ISO","calendarType":"iso8601"},"dayOfWeek":"TUESDAY","leapYear":false,"dayOfYear":12,"era":"CE"},"jmbag":"0025478451","numberOfECTS":55}
    Session Attrs = {}
Handler:
             Type = com.studapp.students.StudentController
           Method = com.studapp.students.StudentController#save(StudentCommand)
MockHttpServletResponse:
           Status = 400
    Error message = null
          Headers = [Vary:"Origin", "Access-Control-Request-Method", "Access-Control-Request-Headers", X-Content-Type-Options:"nosniff", X-XSS-Protection:"1; mode=block", Cache-Control:"no-cache, no-store, max-age=0, must-revalidate", Pragma:"no-cache", Expires:"0", X-Frame-Options:"DENY"]
     Content type = null
             Body = 
    Forwarded URL = null
   Redirected URL = null
          Cookies = []
java.lang.AssertionError: Status expected:<201> but was:<400>
Expected :201
Actual   :400

I am not sure why it fails. Why is response body blank? I dont want to call my service because im not testing it, but i feel like i should call it somehow(but then again, im not testing the service). Any suggestion would be appreciated.

Answer 1

You should use @Autowired on your ObjectMapper to make sure it is configured in the same way by Spring as it would be during the application runtime. This would explain the 400 - Bad request error you are getting.

The fact that it is a 409 - Conflict after autowiring the ObjectMapper suggests that this was indeed the error. Since you do not configure your studentServiceMock in the test, the 409 seems to be the apporiate answer from the controller, because the orElseGet part is being executed.

If I am not mistaken, you could slim down the test class annotations a little and only use @WebMvcTest. This should suffice for this kind of test and it should be a little faster.