[java] How to write a unit test for a Spring Boot Controller endpoint

I have a sample Spring Boot app with the following

Boot main class

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

Controller

@RestController
@EnableAutoConfiguration
public class HelloWorld {
    @RequestMapping("/")
    String gethelloWorld() {
        return "Hello World!";
    }

}

What's the easiest way to write a unit test for the controller? I tried the following but it complains about failing to autowire WebApplicationContext

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = DemoApplication.class)
public class DemoApplicationTests {

    final String BASE_URL = "http://localhost:8080/";

    @Autowired
    private WebApplicationContext wac;

    private MockMvc mockMvc;

    @Before
    public void setup() {
        this.mockMvc = MockMvcBuilders.webAppContextSetup(this.wac).build();
    }

    @Test
    public void testSayHelloWorld() throws Exception{

         this.mockMvc.perform(get("/")
                 .accept(MediaType.parseMediaType("application/json;charset=UTF-8")))
                 .andExpect(status().isOk())
                 .andExpect(content().contentType("application/json"));
    }

    @Test
    public void contextLoads() {
    }

}

Here is another answer using Spring MVC's standaloneSetup. Using this way you can either autowire the controller class or Mock it.

    import static org.mockito.Mockito.mock;
    import static org.springframework.test.web.server.request.MockMvcRequestBuilders.get;
    import static org.springframework.test.web.server.result.MockMvcResultMatchers.content;
    import static org.springframework.test.web.server.result.MockMvcResultMatchers.status;

    import org.junit.Before;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.http.MediaType;
    import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
    import org.springframework.test.web.server.MockMvc;
    import org.springframework.test.web.server.setup.MockMvcBuilders;


    @RunWith(SpringJUnit4ClassRunner.class)
    @SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
    public class DemoApplicationTests {

        final String BASE_URL = "http://localhost:8080/";

        @Autowired
        private HelloWorld controllerToTest;

        private MockMvc mockMvc;

        @Before
        public void setup() {
            this.mockMvc = MockMvcBuilders.standaloneSetup(controllerToTest).build();
        }

        @Test
        public void testSayHelloWorld() throws Exception{
            //Mocking Controller
            controllerToTest = mock(HelloWorld.class);

             this.mockMvc.perform(get("/")
                     .accept(MediaType.parseMediaType("application/json;charset=UTF-8")))
                     .andExpect(status().isOk())
                     .andExpect(content().mimeType(MediaType.APPLICATION_JSON));
        }

        @Test
        public void contextLoads() {
        }

    }

Let assume i am having a RestController with GET/POST/PUT/DELETE operations and i have to write unit test using spring boot.I will just share code of RestController class and respective unit test.Wont be sharing any other related code to the controller ,can have assumption on that.

@RestController
@RequestMapping(value = “/myapi/myApp” , produces = {"application/json"})
public class AppController {


    @Autowired
    private AppService service;

    @GetMapping
    public MyAppResponse<AppEntity> get() throws Exception {

        MyAppResponse<AppEntity> response = new MyAppResponse<AppEntity>();
        service.getApp().stream().forEach(x -> response.addData(x));    
        return response;
    }


    @PostMapping
    public ResponseEntity<HttpStatus> create(@RequestBody AppRequest request) throws Exception {
        //Validation code       
        service.createApp(request);

        return ResponseEntity.ok(HttpStatus.OK);
    }

    @PutMapping
    public ResponseEntity<HttpStatus> update(@RequestBody IDMSRequest request) throws Exception {

        //Validation code
        service.updateApp(request);

        return ResponseEntity.ok(HttpStatus.OK);
    }

    @DeleteMapping
    public ResponseEntity<HttpStatus> delete(@RequestBody AppRequest request) throws Exception {

        //Validation        
        service.deleteApp(request.id);

        return ResponseEntity.ok(HttpStatus.OK);
    }

}

@RunWith(SpringJUnit4ClassRunner.class)
@SpringBootTest(classes = Main.class)
@WebAppConfiguration
public abstract class BaseTest {
   protected MockMvc mvc;
   @Autowired
   WebApplicationContext webApplicationContext;

   protected void setUp() {
      mvc = MockMvcBuilders.webAppContextSetup(webApplicationContext).build();
   }
   protected String mapToJson(Object obj) throws JsonProcessingException {
      ObjectMapper objectMapper = new ObjectMapper();
      return objectMapper.writeValueAsString(obj);
   }
   protected <T> T mapFromJson(String json, Class<T> clazz)
      throws JsonParseException, JsonMappingException, IOException {

      ObjectMapper objectMapper = new ObjectMapper();
      return objectMapper.readValue(json, clazz);
   }
}

public class AppControllerTest extends BaseTest {

    @MockBean
    private IIdmsService service;

    private static final String URI = "/myapi/myApp";


   @Override
   @Before
   public void setUp() {
      super.setUp();
   }

   @Test
   public void testGet() throws Exception {
       AppEntity entity = new AppEntity();
      List<AppEntity> dataList = new ArrayList<AppEntity>();
      AppResponse<AppEntity> dataResponse = new AppResponse<AppEntity>();
      entity.setId(1);
      entity.setCreated_at("2020-02-21 17:01:38.717863");
      entity.setCreated_by(“Abhinav Kr”);
      entity.setModified_at("2020-02-24 17:01:38.717863");
      entity.setModified_by(“Jyoti”);
            dataList.add(entity);

      dataResponse.setData(dataList);

      Mockito.when(service.getApp()).thenReturn(dataList);

      RequestBuilder requestBuilder =  MockMvcRequestBuilders.get(URI)
                 .accept(MediaType.APPLICATION_JSON);

        MvcResult mvcResult = mvc.perform(requestBuilder).andReturn();
        MockHttpServletResponse response = mvcResult.getResponse();

        String expectedJson = this.mapToJson(dataResponse);
        String outputInJson = mvcResult.getResponse().getContentAsString();

        assertEquals(HttpStatus.OK.value(), response.getStatus());
        assertEquals(expectedJson, outputInJson);
   }

   @Test
   public void testCreate() throws Exception {

       AppRequest request = new AppRequest();
       request.createdBy = 1;
       request.AppFullName = “My App”;
       request.appTimezone = “India”;

       String inputInJson = this.mapToJson(request);
       Mockito.doNothing().when(service).createApp(Mockito.any(AppRequest.class));
       service.createApp(request);
       Mockito.verify(service, Mockito.times(1)).createApp(request);

       RequestBuilder requestBuilder =  MockMvcRequestBuilders.post(URI)
                                                             .accept(MediaType.APPLICATION_JSON).content(inputInJson)
                                                             .contentType(MediaType.APPLICATION_JSON);

       MvcResult mvcResult = mvc.perform(requestBuilder).andReturn();
       MockHttpServletResponse response = mvcResult.getResponse();
       assertEquals(HttpStatus.OK.value(), response.getStatus());

   }

   @Test
   public void testUpdate() throws Exception {

       AppRequest request = new AppRequest();
       request.id = 1;
       request.modifiedBy = 1;
        request.AppFullName = “My App”;
       request.appTimezone = “Bharat”;

       String inputInJson = this.mapToJson(request);
       Mockito.doNothing().when(service).updateApp(Mockito.any(AppRequest.class));
       service.updateApp(request);
       Mockito.verify(service, Mockito.times(1)).updateApp(request);

       RequestBuilder requestBuilder =  MockMvcRequestBuilders.put(URI)
                                                             .accept(MediaType.APPLICATION_JSON).content(inputInJson)
                                                             .contentType(MediaType.APPLICATION_JSON);

       MvcResult mvcResult = mvc.perform(requestBuilder).andReturn();
       MockHttpServletResponse response = mvcResult.getResponse();
       assertEquals(HttpStatus.OK.value(), response.getStatus());

   }

   @Test
   public void testDelete() throws Exception {

       AppRequest request = new AppRequest();
       request.id = 1;

       String inputInJson = this.mapToJson(request);
       Mockito.doNothing().when(service).deleteApp(Mockito.any(Integer.class));
       service.deleteApp(request.id);
       Mockito.verify(service, Mockito.times(1)).deleteApp(request.id);

       RequestBuilder requestBuilder =  MockMvcRequestBuilders.delete(URI)
                                                             .accept(MediaType.APPLICATION_JSON).content(inputInJson)
                                                             .contentType(MediaType.APPLICATION_JSON);

       MvcResult mvcResult = mvc.perform(requestBuilder).andReturn();
       MockHttpServletResponse response = mvcResult.getResponse();
       assertEquals(HttpStatus.OK.value(), response.getStatus());

   }

}

Adding @WebAppConfiguration (org.springframework.test.context.web.WebAppConfiguration) annotation to your DemoApplicationTests class will work.

The new testing improvements that debuted in Spring Boot 1.4.M2 can help reduce the amount of code you need to write situation such as these.

The test would look like so:

import static org.springframework.test.web.servlet.request.MockMvcRequestB??uilders.get; 
import static org.springframework.test.web.servlet.result.MockMvcResultMat??chers.content; 
import static org.springframework.test.web.servlet.result.MockMvcResultMat??chers.status;

    @RunWith(SpringRunner.class)
    @WebMvcTest(HelloWorld.class)
    public class UserVehicleControllerTests {

        @Autowired
        private MockMvc mockMvc;

        @Test
        public void testSayHelloWorld() throws Exception {
            this.mockMvc.perform(get("/").accept(MediaType.parseMediaType("application/json;charset=UTF-8")))
                    .andExpect(status().isOk())
                    .andExpect(content().contentType("application/json"));

        }

    }

See this blog post for more details as well as the documentation