Inject mock into Spring MockMvc WebApplicationContext

Here's another solution. Simply put, it just creates a new RestTemplate bean and overrides the one already registered.

So while it performs produces the same functionality as @mzc answer, it allows me to use Mockito to craft the response and verification matchers a bit easier.

Not that it's more than a couple lines of code, but it also prevents from having to add additional code to convert from the Response object to a string for the above mockRestServiceServer.expect().andRespond(<String>) method's arg.

@RunWith(SpringJUnit4ClassRunner.class)
@WebAppConfiguration
@SpringApplicationConfiguration(classes = MainSpringBootAdapter.class)
@TestPropertySource("/application-junit.properties")
public class WacControllerTest {

    private static String Controller_URL = Constants.REQUEST_MAPPING_PATH + Constants.REQUEST_MAPPING_RESOURCE + compressedParams_all;

    @Configuration
        static class Config {
            @Bean
            @Primary
            public RestTemplate restTemplateMock() {
                return Mockito.mock(RestTemplate.class);
        }
    }

    @Autowired
    private WebApplicationContext wac;

    private MockMvc mockMvc;

    @InjectMocks
    private Controller Controller;

    @Mock
    private RestTemplate rt;

    @Value("${file}")
    private String file;

    @Spy
    private DataProvider dp;

    @Before
    public void setup() throws Exception {
        dp = new DataProvider(file); 

        MockitoAnnotations.initMocks(this);
        this.mockMvc = MockMvcBuilders.webAppContextSetup(this.wac).build();
        this.rt = (RestTemplate) this.wac.getBean("restTemplateMock");
    }

    @Test
    public void testGetResponse() throws Exception {

        String[] strings = {"request", "100"};

        //Set the request params from the client request
        Map<String, String> parameters = new HashMap<String, String>();
        parameters.put(Constants.PARAM_SINGLELINE, strings[0]);
        parameters.put(Constants.PARAM_FORMAT, Constants.PARAMS_FORMAT.JSON);

        Mockito.when(
            rt.getForObject(Mockito.<String> any(), Mockito.<Class<Object>> any(), Mockito.<Map<String, ?>> any()))
            .thenReturn(populateTestResponse());

        mockMvc.perform(get(Controller_URL, strings)
            .accept(Constants.APPLICATION_JSON_UTF8))
            .andDo(MockMvcResultHandlers.print());

        Mockito.verify(rt, Mockito.times(1)).getForObject(Mockito.<String> any(), Mockito.<Class<?>> any(), Mockito.<Map<String, ?>> any());

        }


        private Response populateTestResponse() {
            Response  resp = new Response();

            resp.setScore(new BigDecimal(100));
            resp.setData("Some Data");

            return resp;
    }
}

Spring's MockRestServiceServer is exactly what you're looking for.

Short description from javadoc of the class:

Main entry point for client-side REST testing. Used for tests that involve direct or indirect (through client code) use of the RestTemplate. Provides a way to set up fine-grained expectations on the requests that will be performed through the RestTemplate and a way to define the responses to send back removing the need for an actual running server.

Try to set up your test like this:

@WebAppConfiguration
@ContextConfiguration(classes = {YourSpringConfig.class})
@RunWith(SpringJUnit4ClassRunner.class)
public class ExampleResourceTest {

    private MockMvc mockMvc;
    private MockRestServiceServer mockRestServiceServer;

    @Autowired
    private WebApplicationContext wac;

    @Autowired
    private RestOperations restOperations;

    @Before
    public void setUp() throws Exception {
        mockMvc = MockMvcBuilders.webAppContextSetup(this.wac).build();
        mockRestServiceServer = MockRestServiceServer.createServer((RestTemplate) restOperations);
    }


    @Test
    public void testMyApiCall() throws Exception {
        // Following line verifies that our code behind /api/my/endpoint made a REST PUT
        // with expected parameters to remote service successfully
        expectRestCallSuccess();

        this.mockMvc.perform(MockMvcRequestBuilders.get("/api/my/endpoint"))
            .andExpect(status().isOk());
    }

    private void expectRestCallSuccess() {
        mockRestServiceServer.expect(
            requestTo("http://remote.rest.service/api/resource"))
            .andExpect(method(PUT))
            .andRespond(withSuccess("{\"message\": \"hello\"}", APPLICATION_JSON));
    }


}