Unit Test of file upload using MockMvcBuilders with standalone context and SpringBoot 1.2.5

I'm using Spring Boot 1.2.5-RELEASE. I have a controller that receive a MultipartFile and a String

@RestController
@RequestMapping("file-upload")
public class MyRESTController {

  @Autowired
  private AService aService;

  @RequestMapping(method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
  @ResponseStatus(HttpStatus.CREATED)
  public void fileUpload(
      @RequestParam(value = "file", required = true) final MultipartFile file,
      @RequestParam(value = "something", required = true) final String something) {
   aService.doSomethingOnDBWith(file, value);
  }
}

Now, the service works well. I tested it with PostMan and eveything goes as expected. Unfortunately, I cannot write a standalone unit test for that code. The current unit test is:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = MyApplication.class)
@WebAppConfiguration
public class ControllerTest{

    MockMvc mockMvc;

    @Mock
    AService aService;

    @InjectMocks
    MyRESTController controller;

  @Before public void setUp(){
    MockitoAnnotations.initMocks(this);
    this.mockMvc = MockMvcBuilders.standaloneSetup(controller).build();
  }

  @Test
  public void testFileUpload() throws Exception{
        final File file = getFileFromResource(fileName);
        //File is correctly loaded
        final MockMultipartFile multipartFile = new MockMultipartFile("aMultiPartFile.txt", new FileInputStream(file));

        doNothing().when(aService).doSomethingOnDBWith(any(MultipartFile.class), any(String.class));

        mockMvc.perform(
                post("/file-upload")
                        .requestAttr("file", multipartFile.getBytes())
                        .requestAttr("something", ":(")
                        .contentType(MediaType.MULTIPART_FORM_DATA_VALUE))
                .andExpect(status().isCreated());
    }
}

Test fails with

java.lang.IllegalArgumentException: Expected MultipartHttpServletRequest: is a MultipartResolver configured?

Now, in the MultipartAutoConfiguration class from Spring Boot I see that a MultipartResolver is auto configured. But, I guess that with the standaloneSetup of MockMvcBuilders I cannot access this.

I tried several configurations of the unit test that I don't report for brevity. Especially, I also tried rest-assured as shown here, but honestly this doesn't work because it seems that I cannot mock the AService instance.

Any solution?