How to write a unit test for a Spring Boot Controller endpoint

Question

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() {     }  } 

Answer 1

Spring MVC offers a standaloneSetup that supports testing relatively simple controllers, without the need of context.

Build a MockMvc by registering one or more @Controller's instances and configuring Spring MVC infrastructure programmatically. This allows full control over the instantiation and initialization of controllers, and their dependencies, similar to plain unit tests while also making it possible to test one controller at a time.

An example test for your controller can be something as simple as

public class DemoApplicationTests {      private MockMvc mockMvc;      @Before     public void setup() {         this.mockMvc = MockMvcBuilders.standaloneSetup(new HelloWorld()).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"));      } } 

Answer 2

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