Difference between MockMvc and RestTemplate in integration tests

As said in this article you should use MockMvc when you want to test Server-side of application:

Spring MVC Test builds on the mock request and response from spring-test and does not require a running servlet container. The main difference is that actual Spring MVC configuration is loaded through the TestContext framework and that the request is performed by actually invoking the DispatcherServlet and all the same Spring MVC infrastructure that is used at runtime.

for example:

@RunWith(SpringJUnit4ClassRunner.class)
@WebAppConfiguration
@ContextConfiguration("servlet-context.xml")
public class SampleTests {

  @Autowired
  private WebApplicationContext wac;

  private MockMvc mockMvc;

  @Before
  public void setup() {
    this.mockMvc = webAppContextSetup(this.wac).build();
  }

  @Test
  public void getFoo() throws Exception {
    this.mockMvc.perform(get("/foo").accept("application/json"))
        .andExpect(status().isOk())
        .andExpect(content().mimeType("application/json"))
        .andExpect(jsonPath("$.name").value("Lee"));
  }}

And RestTemplate you should use when you want to test Rest Client-side application:

If you have code using the RestTemplate, you’ll probably want to test it and to that you can target a running server or mock the RestTemplate. The client-side REST test support offers a third alternative, which is to use the actual RestTemplate but configure it with a custom ClientHttpRequestFactory that checks expectations against actual requests and returns stub responses.

example:

RestTemplate restTemplate = new RestTemplate();
MockRestServiceServer mockServer = MockRestServiceServer.createServer(restTemplate);

mockServer.expect(requestTo("/greeting"))
  .andRespond(withSuccess("Hello world", "text/plain"));

// use RestTemplate ...

mockServer.verify();

also read this example

With MockMvc, you're typically setting up a whole web application context and mocking the HTTP requests and responses. So, although a fake DispatcherServlet is up and running, simulating how your MVC stack will function, there are no real network connections made.

With RestTemplate, you have to deploy an actual server instance to listen for the HTTP requests you send.