Getting a null pointer when testing a controller using MockMvc

Question

I am getting a null pointer when unit testing a controller. The null pointer is occurring in the controller when calling a mocked service to get an id. I tried many things but I am still getting the same error.

Below is a snippet from the controller code where the null pointer is occurring:

@RestController
@RequestMapping(ELEMENTS_BASE_URI)
@EnableCommonRestHeaders
public class ElementController {
    @Autowired
    private ElementService elementService;
...
public ResponseEntity<ElementDto> createElement(
            @Valid @RequestBody ElementDto elementDto) {

        ElementDto saved = elementService.createElement(elementDto);

        HttpHeaders headers = new HttpHeaders();

        URI location = UriBuilder.builder(ELEMENT_LINK_URI)
                .pathVariable(ELEMENT_ID, saved.getId())
                .create();
        headers.setLocation(location);

        return new ResponseEntity<>(saved, headers, HttpStatus.CREATED);
    }
...

}

In the controller code above, The null pointer occurs at the line below: saved is null

   ElementDto saved = elementService.createElement(elementDto);

The test code is as below:

import static com.sas.fcs.networkbuild.util.matchers.JSONContentResultMatcher.jsonObject;
import static com.sas.fcs.networkbuild.util.matchers.JSONContentResultMatcher.jsonPath;

@RunWith(SpringJUnit4ClassRunner.class)
@WebMvcTest(controllers = ElementController.class, excludeAutoConfiguration = MockMvcSecurityAutoConfiguration.class)
@ActiveProfiles(value = {"test", "hsql", "disable-oauth2"})
@TestPropertySource("classpath:/test.properties")
public class ElementControllerTest {


    @MockBean
    private ElementService elementService;

    @Autowired
    ElementController elementController;

    @Autowired
    private MockMvc mockMvc;

    @Autowired
    private ObjectMapper mapper;

    @Before
    public void setUp() {
        mockMvc = MockMvcBuilders
                .standaloneSetup(elementController)
                .build();
    }

    @Test
    public void testCreateElementSuccess() throws Exception {
        ElementDto element = new ElementDto();
        element.setName("firstname");
        element.setModifiedTimeStamp(new Date());

        ElementDto createdElement = new ElementDto();
        String elementId = "123";
        createdElement.setId(elementId);
        createdElement.setName("firstname");
        createdElement.setLabel("firstname");
        createdElement.setAttribute(true);
        createdElement.setKeep(true);


        when(elementService.create(element)).thenReturn(createdElement);

        // make sure returns location with new element id
        mockMvc.perform(
                post(ServiceConstants.ELEMENTS_BASE_URI)
                     .content(mapper.writeValueAsBytes(element))
                     .accept(ElementDto.MEDIA_TYPE_JSON_VALUE)
                     .contentType(ElementDto.MEDIA_TYPE_JSON_VALUE))
                     .andExpect(status().isCreated())
                     .andExpect(header().string("Location",
                        Matchers.endsWith(ServiceConstants.SERVICE_URI + ServiceConstants.ELEMENTS_BASE_URI + "/" + elementId)))
                     .andExpect(header().string("Last-Modified", not(isEmptyString())))
                     .andExpect(jsonObject().is(createdElement))
                     .andExpect(jsonPath("name").value(element.getName()))
                     .andReturn();
    }
}

The line:

when(elementService.create(element)).thenReturn(createdElement);

does not seem to have any effect. Any help on this is really appreciated.

Regards, Firas

Because `ElementDto` in your test and `ElementDto` in the controller will not be the same instance. I suspect you want to use: `when(elementService.create(Mockito.any())).thenReturn(createdElement);` — Alan Hay, Feb 19 '20 at 16:14
@AlanHay, I replaced it with this line: when(elementService.create(Mockito.any())).thenReturn(createdElement); I am still getting same error. Thanks. — F. K., Feb 19 '20 at 16:18
I also tried the following, but still same issue: when(elementService.create(Mockito.any(ElementDto.class))).thenReturn(createdElement); — F. K., Feb 19 '20 at 16:29
What is it that is actually null, the service or the created item? Your mocking annotations look wrong. See here for examples: https://stackoverflow.com/questions/16170572/unable-to-mock-service-class-in-spring-mvc-controller-tests/33274821 — Alan Hay, Feb 19 '20 at 16:43
@AlanHay as I mentioned in the question, the null is happening at this line: ElementDto saved = elementService.createElement(elementDto); saved is null. Not sure what you mean my mocking notations are wrong. They are standard testing annotations. — F. K., Feb 19 '20 at 17:27

score 0 · Answer 1 · answered Feb 19 '20 at 19:29

The cause for this issue, was a mistake I made. The function is createElement and the when/any was referencing create function.

I changed:

when(elementService.create(eq(element))).thenReturn(createdElement);

to:

when(elementService.createElement(eq(element))).thenReturn(createdElement);

The rest of the code and notations are correct.

Getting a null pointer when testing a controller using MockMvc

1 Answers1