java - How do I mock a REST template exchange?

Question

I have a service in which I need to ask an outside server via rest for some information:

public class SomeService {

    public List<ObjectA> getListofObjectsA() {
        List<ObjectA> objectAList = new ArrayList<ObjectA>();
        ParameterizedTypeReference<List<ObjectA>> typeRef = new ParameterizedTypeReference<List<ObjectA>>() {};
        ResponseEntity<List<ObjectA>> responseEntity = restTemplate.exchange("/objects/get-objectA", HttpMethod.POST, new HttpEntity<>(ObjectAList), typeRef);
        return responseEntity.getBody();
    }
}

How can I write a JUnit test for getListofObjectsA()?

I have tried with the below:

@RunWith(MockitoJUnitRunner.class)
public class SomeServiceTest {
    private MockRestServiceServer mockServer;

    @Mock
    private RestTemplate restTemplate;

    @Inject
   private SomeService underTest;

@Before
public void setup() {
    mockServer = MockRestServiceServer.createServer(restTemplate);
    underTest = new SomeService(restTemplate);
    mockServer.expect(requestTo("/objects/get-objectA")).andExpect(method(HttpMethod.POST))
            .andRespond(withSuccess("{json list response}", MediaType.APPLICATION_JSON));
}

    @Test
    public void testGetObjectAList() {
    List<ObjectA> res = underTest.getListofObjectsA();
    Assert.assertEquals(myobjectA, res.get(0));
}

However the above code does not work, it shows that responseEntitty is null. How can I correct my test to properly mock restTemplate.exchange?

Answer 1

You don't need MockRestServiceServer object. The annotation is @InjectMocks not @Inject. Below is an example code that should work

@RunWith(MockitoJUnitRunner.class)
public class SomeServiceTest {
    @Mock
    private RestTemplate restTemplate;

    @InjectMocks
    private SomeService underTest;

    @Test
    public void testGetObjectAList() {
        ObjectA myobjectA = new ObjectA();
        //define the entity you want the exchange to return
        ResponseEntity<List<ObjectA>> myEntity = new ResponseEntity<List<ObjectA>>(HttpStatus.ACCEPTED);
        Mockito.when(restTemplate.exchange(
            Matchers.eq("/objects/get-objectA"),
            Matchers.eq(HttpMethod.POST),
            Matchers.<HttpEntity<List<ObjectA>>>any(),
            Matchers.<ParameterizedTypeReference<List<ObjectA>>>any())
        ).thenReturn(myEntity);

        List<ObjectA> res = underTest.getListofObjectsA();
        Assert.assertEquals(myobjectA, res.get(0));
    }