Spring 5 with JUnit 5 + Mockito - Controller metho

Question

I try to test a method named as loadData defined in MainController which returns result as a string. Despite that this method actually returns data when the web app runs on servlet container (or when I debug the code), no data returns when I invoke it from a test class based on JUnit 5 with Mockito.

Here is my configuration:

@ContextConfiguration(classes = {WebAppInitializer.class, AppConfig.class, WebConfig.class})
@Transactional
@WebAppConfiguration
public class TestMainController {

    @InjectMocks
    private MainController mainController;

    private MockMvc mockMvc;

    @BeforeEach
    public void init() {
        mockMvc = MockMvcBuilders.standaloneSetup(this.mainController).build();
    }

    @Test
    public void testLoadData() throws Exception {
        MvcResult mvcResult = mockMvc
                .perform(MockMvcRequestBuilders.get("/loadData.ajax"))
                .andExpect(MockMvcResultMatchers.status().isOk()).andReturn();

        Assertions.assertNotNull(mvcResult.getResponse().getContentAsString(), "response should not be null");
    }

}

The test fails due to java.lang.NullPointerException as the this.mainController is null.

Environment Details:

Spring version: 5.0.3
JUnit version: 5.0.3
mockito version: 1.9.5
hamcrest version: 1.3
json-path-assert version: 2.2.0

Edit: Here is the loadData method of MainController:

@RequestMapping(value = "/loadData.ajax", method = RequestMethod.GET)
public String loadData(HttpServletRequest request, HttpServletResponse response) {
    List list = mainService.loadData(); // starts a transaction and invokes the loadData method of mainDAO repository which basically loads data from the database
    return JSONArray.fromObject(list).toString();
}

Answer 1

You can call controller method directly, just like we do for service method, but this is not recommended. Using MockMvc, you check for header and request param mapping are proper. Plus, you also check for end point mapping is correct. Plus the Request METHOD is also correct. All these you cannot test if you test your code by directly calling the controller method.

One thing you can try is, instead of creating new object inside the standalone context, use the Mock. i.e

mockMvc = MockMvcBuilders.standaloneSetup(this. mainController).build();

And while calling, do this

MvcResult mvcResult = mockMvc
    .perform(MockMvcRequestBuilders.get("/loadData.ajax"))
    .andExpect(MockMvcResultMatchers.status().isOk()).andReturn();

Assert , what you would like to

Assert.assertEquals("response does not match", mvcResult.getResponse().getContentAsString(),
    "some expected response");

You are getting null or 400 or 404 http status ?

If you are getting 400, then please check the header and req. param if any are proper. If you are getting 404 then please check the URL path. /loadData.ajax , assuming this is your request mapping path in controller method.