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));     } 

Answer 2

This is an example with the non deprecated ArgumentMatchers class

when(restTemplate.exchange(                 ArgumentMatchers.anyString(),                 ArgumentMatchers.any(HttpMethod.class),                 ArgumentMatchers.any(),                 ArgumentMatchers.<Class<String>>any()))              .thenReturn(responseEntity);