How to test a Spring REST consumer with JUnit

I'm creating a Java Spring based microservice application that communicates using REST endpoints.

The app itself is so far has a simple structure: UI <-> DBLayer. The UI module is a api consumer and DBLayer is an api provider.

That being said I would like to test if my UI makes the correct REST calls using JUnit and/or Mockito. To be more specific, say I have a service class like this:

@Service
public class AuthorityService {

    @Autowired
    private RestTemplate restTemplate;

    public Authority getAuthority(String authorityName) {
        Authority authority = 
               restTemplate.getForObject(
                  "http://localhost:8080/authorities/" + authorityName,
                   Authority.class);           
        return authority;
    }
}

In order to test this service method I would like to somehow verify that exactly this endpoint was called. Is there a way to wrap the service method and somehow assert a rest GET/POST/PUT etc. calls being made?

The desired test class should look something like this:

public class AuthorityServiceTest {
    private AuthorityService authorityService = new AuthorityService();

    @Test
    public void getAuthorityTest(){
        Assert.assertHttpGETCallMade(
                authorityService.getAuthority("test"),
                "http://localhost:8080/authorities/test");
    }
}

Solution

You can use Mockito to inject the template, then verify the call.

@ExtendWith(MockitoExtension.class) // RunWith(MockitoJUnitRunner.class) for JUnit 4
public class AuthorityServiceTest {
    @InjectMocks
    private AuthorityService sut;

    @Mock RestTemplate restTemplate;

    @Test
    public void getAuthorityTest(){
        // mock rest call
        Authority auth = mock(Authority.class);
        when(restTemplate.getForObject(any(String.class), any(Class.class)).thenReturn(auth);

        Authority result = sut.getAuthority("test");

        // verify mock result was returned
        assertSame(auth, result);
        // verify call to rest template was performed
        verify(restTemplate).getForObject(
              "http://localhost:8080/authorities/test",
               Authority.class);
    }
}