spring-async-controller-test.java

/**
 *  Spring controller method using async features.Controller method to handle POST.requests. It will set 'Location' header and set HTTP status to 201. 
 */
 @RequestMapping(method = RequestMethod.POST, consumes = {MediaType.APPLICATION_JSON_VALUE, MediaType.APPLICATION_XML_VALUE})
    public Callable<ResponseEntity<Void>> userSignup(@RequestBody User user, HttpServletResponse response, HttpServletRequest request) {
        return () -> {
            String id = userService.createUser(user);
            HttpHeaders headers = new HttpHeaders();
            headers.setLocation(new URI("http://myhost.com/users/id/" + id)));
            return new ResponseEntity<>(headers, HttpStatus.CREATED);
        };

    }
    
    /**
     * Test case for the method above. It uses SPring MockMvc for controller testing.
     */
     @Test
    public void createUserTest() throws Exception{
        User user = new User();
        user.setFirstname("John");
        user.setLastname("Doe");
        user.setEmail("user@mail.com");
        user.setPassword("password");
        JAXBContext ctx = JAXBContext.newInstance(User.class);
        Marshaller marshaller = ctx.createMarshaller();
        StringWriter writer = new StringWriter();
        marshaller.marshal(user, writer);
        writer.close();
        System.out.println("XML: " + writer.toString());
        MvcResult result = mockMvc.perform(post("/users").content(writer.toString()).contentType("application/xml")).andExpect(request().asyncStarted()).andReturn();
        mockMvc.perform(asyncDispatch(result)).andExpect(status().isCreated()).andExpect(header().string("Location",org.hamcrest.Matchers.startsWith("http://localhost:80/users/id"))).andDo(print()).andReturn();
        
    }

How can I test if controller call an async service method like below?

CONTROLLER

@RequestMapping(method = RequestMethod.POST, consumes = {MediaType.APPLICATION_JSON_VALUE, MediaType.APPLICATION_XML_VALUE})
    public ResponseEntity<Void> userSignup(@RequestBody User user, HttpServletResponse response, HttpServletRequest request) {
            userService.createUser(user);
            HttpHeaders headers = new HttpHeaders();
            headers.setLocation(new URI("http://myhost.com/wlcome_page")));
            return new ResponseEntity<>(headers, HttpStatus.CREATED);
        }

SERVICE

@Async
    public Future<User> createUser(User user) Exception {
        user = userRepository.save(user);
        return new AsyncResult<>(user);
    }