[FIXED] I have an error "Content type not set" when testing with junit

Issue

I use spring boot 2.7 and test with junit during the execution of the tests I get an error : the other tests work well.

controller

@PostMapping(value = "/employees")
public ResponseEntity<Employee> addEmployee(@Valid @RequestBody EmployeeDto employeeDto) {

    Optional<Employee> employeeDb = employeeService.findByEmail(employeeDto.getEmail());

    // must not exist in database
    if (!employeeDb.isEmpty()) {
        return new ResponseEntity<>(HttpStatus.CONFLICT);
    }

    // convertion dto -> model
    Employee employee = employeeDto.toEmployee();

    return new ResponseEntity<>(employeeService.save(employee), HttpStatus.OK);
}

controllerTest

@Test
void addEmployee() throws Exception {

    when(employeeService.save(employeeDto.toEmployee())).thenReturn(employee);
    when(employeeService.findByEmail(any(String.class))).thenReturn(Optional.of(employee));

    ObjectMapper objectMapper = new ObjectMapper();
    String json = objectMapper.writeValueAsString(employeeDto);

    mockMvc.perform(
        MockMvcRequestBuilders
        .post(REST_URL)
        .contentType(MediaType.APPLICATION_JSON)
        .accept(MediaType.APPLICATION_JSON)
        .characterEncoding("utf-8")
        .content(json)
    )
    .andExpect(status().isOk())
    .andExpect(content().contentTypeCompatibleWith(MediaType.APPLICATION_JSON))
    .andExpect(jsonPath("$.firstname", is(employee.getFirstname())))
    .andExpect(jsonPath("$.lastname", is(employee.getLastname())))
    .andExpect(jsonPath("$.email", is(employee.getEmail())));
}

the error : "Content type not set" yet in the test I indicate well the content-type : ".contentType(MediaType.APPLICATION_JSON)"

MockHttpServletRequest:
      HTTP Method = POST
      Request URI = /api/employees/
       Parameters = {}
          Headers = [Content-Type:"application/json;charset=UTF-8", Accept:"application/json", Content-Length:"74"]
             Body = {"email":"[email protected]","firstname":"firstname1","lastname":"lastname1"}
    Session Attrs = {}

Handler:
             Type = com.acme.app1.controllers.EmployeeController
           Method = com.acme.app1.controllers.EmployeeController#addEmployee(EmployeeDto)

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 = []

java.lang.AssertionError: Content type not set

    at org.springframework.test.util.AssertionErrors.fail(AssertionErrors.java:37)
    at org.springframework.test.util.AssertionErrors.assertTrue(AssertionErrors.java:70)
    at org.springframework.test.util.AssertionErrors.assertNotNull(AssertionErrors.java:106)

for the test to be successful, what should I change?

Solution

The content type you've set is used for the request, but in your assertion you're checking for the content type which is returned in the response.

As you can see in the log, there is no content type or body set in the MockHttpServletResponse:

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

Redirected URL = null Cookies = []

So there seems to be an issue with the returned object in your mocked result of

when(employeeService.save(employeeDto.toEmployee())).thenReturn(employee);

since the result of this will be rendered to a JSON object you're doing your assertions on.

Answered By - Stefan Billmaier
Answer Checked By - Timothy Miller (JavaFixing Admin)