Spring Boot: REST controller Test example


updated 02.2022

In my Spring Boot - Angular showcase you can find some examples of REST controller tests.

The @RestController used for the example is the following:

@RestController 
// we allow cors requests from our frontend environment 
// note the curly braces that create an array of strings ... required by the annotation 
@CrossOrigin(origins =  {"${app.dev.frontend.local"}) 
public class HelloController { 
 
  // simple GET response for our example purpose, we return a JSON structure 
  @RequestMapping(value = "/message", produces = MediaType.APPLICATION_JSON_VALUE) 
  public Map<String, String> index() { 
    return Collections.singletonMap("message", "Greetings from Spring Boot!"); 
  } 
} 

Test the controller using an embedded server (integration tests)

With this approach, Spring starts an embedded server to test your REST service.

To create these tests you have to add a dependency to :

<dependency> 
  <groupId>org.springframework.boot</groupId> 
  <artifactId>spring-boot-starter-test</artifactId> 
</dependency> 

In your test, you have to define a webEnvironment, in our case we create an environment with a random port number.

Defining the webEnvironment we can wire the TestRestTemplate that allows us to execute REST requests.
TestRestTemplate is fault-tolerant and can be used with Basic authentication headers. It doesn't extend RestTemplateif you encounter issues during r tests you should maybe try RestTemplate.

/** 
 * The goal of this class is to show how the Embedded Server is used to test the REST service 
 */ 
 
// SpringBootTest launch an instance of our application for tests purposes 
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT) 
class HelloControllerEmbeddedServerTest { 
  @Autowired 
  private HelloController helloController; 
 
  // inject the runtime port, it requires the webEnvironment 
  @LocalServerPort 
  private int port; 
 
  // we use TestRestTemplate, it's an alternative to RestTemplate specific for tests 
  // to use this template a webEnvironment is mandatory 
  @Autowired 
  private TestRestTemplate restTemplate; 
 
  @Test 
  void index() { 
    // we test that our controller is not null 
    Assertions.assertThat(helloController).isNotNull(); 
  } 
 
  @Test 
  void indexResultTest() { 
    Assertions.assertThat(restTemplate 
      .getForObject("http://localhost:" + port + "/message", String.class)).contains("from Spring Boot"); 
  } 
} 

When you run the test you can notice in your console that Spring Boot runs a Tomcat Server.

INFO 4230 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 0 (http) 
INFO 4230 --- [main] o.apache.catalina.core.StandardService   : Starting service [Tomcat] 
INFO 4230 --- [main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.43] 
INFO 4230 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext 
INFO 4230 --- [main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1761 ms 

If you are trying to test GET methods with payload, this method could give you headaches.

RestTemplateTest doesn't like to add payloads to the GET request and you will receive an error response, you can read more in my post about the Spring Boot GET Test limitation.

MockMvc, testing without an embedded server

The previous controller could be tested with @MockMvc, this allows us to have tested the RestController without the overhead of a server (pushing us in the integration tests domain).

/** 
 * The goal of this class is to test the controller using a MockMvc object without an embedded server 
 */ 
@SpringBootTest 
@AutoConfigureMockMvc // we mock the http request and we don't need a server 
public class HelloControllerMockMvcTest { 
 
    @Autowired 
    private MockMvc mockMvc; // injected with @AutoConfigureMockMvc 
 
    @Test 
    public void shouldReturnOurText() throws Exception { 
        this.mockMvc 
                .perform(get("/message")) // perform a request that can be chained 
                .andDo(print()) // we log the result 
                .andExpect(content().string(containsString(" from Spring"))); // we check that the Body of the answer contains our expectation 
    } 
} 

In this case Spring initializes a test Servlet without embedding a full server, from the console:

INFO 4589 --- [main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor' 
INFO 4589 --- [main] o.s.b.a.w.s.WelcomePageHandlerMapping    : Adding welcome page: class path resource [static/index.html] 
INFO 4589 --- [main] o.s.b.t.m.w.SpringBootMockServletContext : Initializing Spring TestDispatcherServlet '' 
INFO 4589 --- [main] o.s.t.web.servlet.TestDispatcherServlet  : Initializing Servlet '' 
INFO 4589 --- [main] o.s.t.web.servlet.TestDispatcherServlet  : Completed initialization in 0 ms 

With the .andDo(print()) instruction many details are printed in the console (extract):

... 
ModelAndView: 
        View name = null 
             View = null 
            Model = null 
 
FlashMap: 
       Attributes = null 
 
MockHttpServletResponse: 
           Status = 200 
    Error message = null 
          Headers = [Vary:"Origin", "Access-Control-Request-Method", "Access-Control-Request-Headers", Content-Type:"application/json"] 
     Content type = application/json 
             Body = {"message":"Greetings from Spring Boot!"} 
... 

(Old) Deep dive: @WebMvcTest, how it works

The annotation @WebMvcTest configure only the components that usually interest the web development.

As shown in the image @Service and @Repositoryare not configured.

When we call the @Service from the @Controller we return the mocked object.

Controller example

This is a very simple controller that calls a service and returns a custom object containing a text value:

 
@RestController 
public class SimpleController { 
 
    private SimpleService simpleService; 
 
    public SimpleController(SimpleService simpleService) { 
        this.simpleService = simpleService; 
    } 
 
    @GetMapping(value = "/simple",produces = MediaType.APPLICATION_JSON_VALUE) 
    public ResponseEntity<StringJsonObject> simpleResult() { 
        return ResponseEntity.ok(simpleService.getText()); 
    } 
} 

Here the service code:

 
@Service 
public class SimpleServiceImpl implements SimpleService{ 
    @Override 
    public StringJsonObject getText(){ 
        return new StringJsonObject("Cool!"); 
    } 
} 

The returned object:

public class StringJsonObject { 
 
    private String content; 
 
    public StringJsonObject(String content) { 
        this.content = content; 
    } 
 
    public String getContent() { 
        return content; 
    } 
} 

The test with comments

Here the code used to test the controller:

 
// SpringRunner is an alias of SpringJUnit4ClassRunner 
// it's a Spring extension of JUnit that handles the TestContext 
@RunWith(SpringRunner.class) 
 
// we test only the SimpleController 
@WebMvcTest(SimpleController.class) 
 
public class SimpleControllerTest { 
 
    // we inject the server side Spring MVC test support 
    @Autowired 
    private MockMvc mockMvc; 
 
    // we mock the service, here we test only the controller 
    // @MockBean is a Spring annotation that depends on mockito framework 
    @MockBean 
    private SimpleService simpleServiceMocked; 
 
    @Test 
    public void simpleResult() throws Exception { 
 
        // this is the expected JSON answer 
        String responseBody = "{\"content\":\"Hello World from Spring!\"}"; 
 
        // we set the result of the mocked service 
        given(simpleServiceMocked.getText()) 
                .willReturn(new StringJsonObject("Hello World from Spring!")); 
 
        // the test is executed: 
        // perform: it executes the request and returns a ResultActions object 
        // accept: type of media accepted as response 
        // andExpect: ResultMatcher object that defines some expectations 
        this.mockMvc.perform(get("/simple") 
                .accept(MediaType.APPLICATION_JSON)) 
                .andExpect(status().isOk()) 
                .andExpect(content().string(responseBody)); 
    } 
} 
 

You could be interested in

Spring Boot RestTemplate: test GET request with JSON body is not working

How to test your REST GET controller with Spring Boot
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How to configure a fullstack Angular and Spring Boot application
2018-04-26

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