Java @PutMapping MockHttpServletResponse 的 JUnit RestControllerTest 正文为空

我被一个控制器单元测试put方法卡住了，它总是返回一个空体响应.

下面是我的代码:

雇员服务公司.班

@Override
public Employee updateEmployee(Long id, Employee employee) {
    Employee existingEmployee = employeeRepository.findById(id)
            .orElseThrow(() -> new ResourceNotFoundException("employee with id: " + id + " does not exist."));

    existingEmployee.setFirstName(employee.getFirstName());
    existingEmployee.setLastName(employee.getLastName());
    existingEmployee.setEmail(employee.getEmail());

    return employeeRepository.save(existingEmployee);
}

雇员控制员.具有@RequestMapping("/api/employees")的类

@PutMapping("/{id}")
public ResponseEntity<Employee> updateEmployee(@PathVariable Long id, @RequestBody Employee employee) {
    return new ResponseEntity<>(employeeService.updateEmployee(id, employee), HttpStatus.OK);
}

员工控制测试.班

@Test
public void givenUpdatedEmployee_whenUpdateEmployee_thenReturnUpdatedEmployee() throws Exception {

    Long employeeId = 1L;

    Employee savedEmployee = Employee.builder()
            .id(employeeId)
            .firstName("Jay")
            .lastName("Lai")
            .email("jay@gmail.com")
            .build();

    Employee updatedEmployee = Employee.builder()
            .id(employeeId)
            .firstName("Jayyy")
            .lastName("Laiii")
            .email("jayyy@gmail.com")
            .build();

    BDDMockito.given(employeeService.getEmployeeBYId(employeeId))
            .willReturn(savedEmployee);

    BDDMockito.given(employeeService.updateEmployee(employeeId, updatedEmployee))
            .willReturn(updatedEmployee);

    ResultActions response = mockMvc.perform(MockMvcRequestBuilders.put("/api/employees/{id}", employeeId)
            .contentType(MediaType.APPLICATION_JSON)
            .content(mapper.writeValueAsString(updatedEmployee)));


    response.andDo(MockMvcResultHandlers.print())
            .andExpect(MockMvcResultMatchers.jsonPath("$.firstName", CoreMatchers.is(updatedEmployee.getFirstName())))
            .andExpect(MockMvcResultMatchers.jsonPath("$.lastName", CoreMatchers.is(updatedEmployee.getLastName())))
            .andExpect(MockMvcResultMatchers.jsonPath("$.email", CoreMatchers.is(updatedEmployee.getEmail())));
}

这是输出.

我真的不明白我错过了什么，任何帮助都将不胜感激，谢谢.

MockHttpServletRequest:
  HTTP Method = PUT
  Request URI = /api/employees/1
   Parameters = {}
      Headers = [Content-Type:"application/json;charset=UTF-8", Content-Length:"73"]
         Body = {"id":1,"firstName":"Jayyy","lastName":"Laiii","email":"jayyy@gmail.com"}
Session Attrs = {}

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: No value at JSON path "$.firstName"**