MockMvc perform(post()) test fails with NullPointerException

Question

I have the following controller

@RequestMapping("/locations")
@AllArgsConstructor
@RestController
public class LocationController {

    private final LocationService locationService;

    @PostMapping
    public ResponseEntity<LocationDTO> createLocation(@Valid @RequestBody LocationDTO locationDTO) {

        Location location = locationService.createLocation(toLocation(locationDTO));

        URI uri = ServletUriComponentsBuilder.fromCurrentRequest()
                                             .path("/{id}")
                                             .buildAndExpand(location.getId())
                                             .toUri();

        return ResponseEntity.created(uri).body(toDTO(location));
    }

    //other methods
}

and the tests

@WebMvcTest(LocationController.class)
class LocationControllerTest {

    @Autowired
    private MockMvc mvc;

    @Autowired
    private ObjectMapper objectMapper;

    @MockBean
    private LocationService locationService;

    @MockBean
    private MappingMongoConverter mappingMongoConverter;

    @WithMockUser(value = "test")
    @Test
    void createLocation() throws Exception {

        GeoJsonPoint testGeoJsonPoint = new GeoJsonPoint(123, 123);
        LocationProperties testLocationProperties = new LocationProperties("testName", "testDesc");
        Location testLocation = new Location("testId", testGeoJsonPoint, testLocationProperties);
        String locationDTOString = objectMapper.writeValueAsString(toDTO(testLocation));

        mvc.perform(post("/locations")
                .contentType(APPLICATION_JSON)
                .content(locationDTOString)
                .characterEncoding("utf-8"))
           .andDo(print())
           .andExpect(status().isCreated())
           .andExpect(content().contentType(APPLICATION_JSON))
           .andExpect(content().json(locationDTOString))
           .andExpect(header().string("uri", "http://localhost:8080/api/locations/testId"));
    }
}

Test results: Resolved Exception: Type = java.lang.NullPointerException

java.lang.AssertionError: Status expected:<201> but was:<500> Expected :201 Actual :500

Seems like Location location = locationService.createLocation(toLocation(locationDTO)); this location is set to null. How do I fix this? Any help is appreciated.

Answer 1

I had to mock the behavior of the service since its a mockBean

when(locationService.createLocation(any())).thenReturn(testLocation);

Answer 2

The mocked LocationService is probably returning null (it does in my test). For this test, the LocationService should be a real instance of the Location Service and not a mock.