Junit for resttemplate in a non spring application

Question

I am working on a non-spring application and using restTemplate feature from spring-web.While writing Junit test i am unable to mock response from restTemplate.postForEntity(). What am i doing wrong here.

Below is the function

public JsonObject apiResponse(Request request) throws JsonProcessingException {
            String queryRequest = objectMapper.writeValueAsString(request);
            HttpHeaders headers = new HttpHeaders();
            headers.add("content-type", "application/json");
            RestTemplate restTemplate = new RestTemplate();
            ResponseEntity<String> responseEntity = restTemplate.postForEntity(
                "https://testurl/test/",
                new HttpEntity<>(queryRequest, headers), String.class);

        return JsonParser.parseString(Objects.requireNonNull(responseEntity.getBody())).getAsJsonObject();

Below is the Junit

@ExtendWith(MockitoExtension.class)
public class HandlerTest {

        @Spy
        @InjectMocks
        Handler handler;

        @Mock
        RestTemplate restTemplate;

        @Test
        public void apiREsponseTest() throws JsonProcessingException {

       //this is not  working     
       Mockito.doReturn(new ResponseEntity <>("test", HttpStatus.OK))
                    .when(restTemplate).postForEntity(eq("test"), eq(HttpEntity.class), eq(String.class)); 
            
       assertNotNull(handler.apiResponse(request));

Answer 1

RestTemplate restTemplate = new RestTemplate(); This is not getting mocked as it's a local object and it will always call the real method. You can try this to mock the restTemplate:

RestTemplate restTemplate = getRestTemplate();

protected RestTemplate getRestTemplate() {
    return new RestTemplate();
 }
//Add this stub to your test
when(handler.getRestTemplate()).thenReturn(restTemplate);

The URL is hardcoded here:

ResponseEntity<String> responseEntity = restTemplate.postForEntity(
                "https://testurl/test/",
                new HttpEntity<>(queryRequest, headers), String.class);

Hence the you need to change your stubbing as well.

Mockito.doReturn(new ResponseEntity <>("test", HttpStatus.OK))
                    .when(restTemplate).postForEntity(eq("https://testurl/test/"), eq(HttpEntity.class), eq(String.class));

Making these changes should make your test green hopefully. Let me know if this doesn't resolve your issue.