Spring boot application fails on mockmvc test - spring-mvc

Question

I have a simple controller test that looks like this
#RunWith(SpringJUnit4ClassRunner.class)
#SpringApplicationConfiguration(classes = CuponzaApiApplication.class)
#WebAppConfiguration
public class UserControllerTest {
private MockMvc mockMvc;
#Autowired
protected WebApplicationContext wac;
#Autowired
UserRepository userRepository;
#Before
public void setUp(){
mockMvc = MockMvcBuilders.webAppContextSetup(wac).build();
}
#Test
public void createUser() throws Exception{
CuponzaUser user = new CuponzaUser("some#test.com", "firstName", "lastName");
ObjectWriter jackson = new ObjectMapper().writer().withDefaultPrettyPrinter();
mockMvc.perform(post("/user/add").content(jackson.writeValueAsString(user)).contentType(MediaType.APPLICATION_JSON))
.andDo(print())
.andExpect(status().isOk())
.andExpect(content().contentType("application/json"));
}
however it fails saying the following
java.lang.AssertionError: Content type not set
here is my controller
#RestController
public class UserController {
#Autowired
UserRepository userRepository;
#RequestMapping(value = "/user/add",method = RequestMethod.POST,produces={MediaType.APPLICATION_JSON_VALUE})
public void AddUser(#RequestBody CuponzaUser user, HttpServletResponse response){
if(user ==null){
response.setStatus(HttpStatus.BAD_REQUEST.value());
return;
}else{
user.setCreationDate(new Date());
user.setLastSeenDate(new Date());
userRepository.save(user);
//response.addHeader("Content-Type", MediaType.APPLICATION_JSON_VALUE);
return;
}
}
I dont want to manually add the content type header for each response , and i thought that the "produces" annotation should take care of this
any ideas?

Answer 1

This tends to be a little confusing - produces parameter of a #RequestMapping annotation does not really modify the response header, it is a way to narrow down the appropriate handler method based on the Accept header that the user has specified. Think of it this way, #RequestMapping and all the parameters associated with it is just a way to filter down to the appropriate method for Spring MVC to call.
The MessageConverter responsible for converting the responses to the appropriate media type does plug in the response Content-Type header, I think the issue in your case is because you are not setting the Accept header in your mock test - .accept(MediaType.APPLICATION_JSON)

Answer 2

The issue is that you're not returning anything. Your response body is empty.
In a way it makes sense, there is no content, what would be the point in defining a Content-Type? Setting the Accept header also won't get you anywhere. Furthermore, you should be able to reproduce this same behaviour outside of your unit tests too, i.e. it's not an issue with your unit test/mock setup.
You could either:
return some content
consider returning a 204 (No Content), if you really don't want to return anything (still wouldn't give you a Content-Type header but it would make clear that there is no content)
add the header manually as in the workaround commented out in your question