@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
@AutoConfigureMockMvc
public class MockRestServiceServerTest {
   @Autowired
   private MockMvc mvc;

   @Autowired
   private RestTemplate restTemplate;

   private MockRestServiceServer mockServer;

   @Before
   public void initmock() {
      this.mockServer = MockRestServiceServer.bindTo(restTemplate).ignoreExpectOrder(true).build();
   }

   @After
   public void verify() {
      //this should let the test fail, but does not
      mockServer.verify();
   }

   @Test
   public void test() throws Exception {
      mockServer.expect(once(), requestTo("/remoteurl")).andRespond(withSuccess());
      mvc.perform(MockMvcRequestBuilders
            .post("/test"))
            .andExpect(status().isOk());
   }
} 

@RestController
public class TestServlet {
   @Autowired
   private RestTemplate restTemplate;

   @PostMapping("/test")
   public String test() {
      //simulate 3 concurrent requests
      List<String> requests = new ArrayList<>();
      requests.add("");
      requests.add("");
      requests.add("");

      final AtomicInteger counter = new AtomicInteger(1);

      List<CompletableFuture<ResponseEntity<String>>> futures =
            requests.stream()
                  .map(hostReq ->
                     CompletableFuture.supplyAsync(
                        () -> {
                           System.out.println("sending remote request: " + counter.getAndIncrement());
                           return restTemplate.postForEntity("/remoteurl", null, String.class);
                        })
                        .exceptionally(ex -> {
                           System.out.println("ignoring ex");
                           return null; //ignoring exceptions
                        }))
                  .collect(Collectors.toList());

      futures.stream()
            .map(CompletableFuture::join)
            .filter(Objects::nonNull)
            .collect(Collectors.toList());

      return "OK";
   }
}