@PostMapping("/auth/signup")
public ResponseEntity<RestResponse> registerUser(@Valid @RequestBody SignUpRequest signUpRequest,
                                                     UriComponentsBuilder uriComponentsBuilder)  {
    RestResponse restResponse = this.userService.register(signUpRequest);
    UriComponents uriComponents = uriComponentsBuilder.path("/users").buildAndExpand();
    return ResponseEntity.created(uriComponents.toUri()).body(restResponse);
}

{
    "status": "Created",
    "code": 201,
    "message": "User registered successfully",
    "result": "5bcf8a0487b89823a8ba5628"
}

@RunWith(MockitoJUnitRunner.class)
public class UserControllerTest {

    private MockMvc mockMvc;
    @Mock
    private UserService userService;
    @InjectMocks
    private UserController userController;
    private SignUpRequest signUpRequest;
    private String signupJson;

    @Before
    public void setUp() {
        // initialise signUpRequest object with dummy data
        this.signUpRequest = DummyData.dummySignupRequest();
        // initialise signUpRequest object with dummy data
        this.signupJson = "{"name":"Ayoub Khial","email":"Ayouub.Khial@gmail.com","password":"123456"}";

        mockMvc = MockMvcBuilders.standaloneSetup(userController).build();
    }

    @Test
    public void justATest() throws Exception {
        RestResponse restResponse = new RestResponse<>(HTTPCode.CREATED.getValue(), HTTPCode.CREATED.getKey(),
                "User registered successfully", null);
        given(this.userService.register(this.signUpRequest)).willReturn(restResponse);

        MockHttpServletResponse response = mockMvc.perform(post("/api/auth/signup")
                        .contentType(MediaType.APPLICATION_JSON)
                .content(signupJson))
                .andReturn()
                .getResponse();
        System.out.println(response.getContentAsString());

    }
}

response.getBody()