test Spring RESTful put method failed using MockMVC

I want to use Unit Test for my RESTful API based on Spring Framework, I used mysql to save my data and using PagingAndSortingRepository to implemented with my RESTful API, and this is my test code:

    @RunWith(SpringJUnit4ClassRunner.class)
    @SpringApplicationConfiguration(classes = SpringMvcApplication.class)
    @WebAppConfiguration
    public class CustomerRepositoryTests {


        private MediaType contentType = new MediaType(MediaType.APPLICATION_JSON.getType(),
        SUBTYPE);

        private static final String SUBTYPE = "hal+json";

        private MockMvc mockMvc;
        @Autowired
        private WebApplicationContext webApplicationContext;

        @Autowired
        private CustomerRepository customerRepository;

        private long setupId;

        @Before
        public void setup() {
            this.mockMvc = webAppContextSetup(webApplicationContext)
            .apply(springSecurity())
            .build();
            customerRepository.deleteAll();
            Customer customer = customerRepository.save(new Customer("userId", "my mobile", "my address", "my contactName"));
            setupId = customer.getId();
        }


        @Test
        //// FIXME: 6/26/16 Status Code is always 204, not 200!
        public void changeCustomer() throws Exception {
            mockMvc.perform(put("/api" + "/customers/{id}", setupId)
            .content(TestUtil.objToJson(new Customer("my new userId", "my new mobile", "my new address", "my new contactName")))
            .contentType(contentType))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.userId", is("my new userId")))
            .andExpect(jsonPath("$.contactName", is("my new contactName")))
            .andExpect(jsonPath("$.mobile", is("my new mobile")))
            .andExpect(jsonPath("$.address", is("my new address")));
        }
}

my test always failed and says:

    java.lang.AssertionError: Status 
    Expected :200
    Actual   :204

but when I run my application and use a command like:

     curl -X PUT -H "Content-Type:application/hal+json" -d '{ "userId": "Bilbo", "mobile": "Baggins", "contactName":"my new contact", "address":"new address" }' http://localhost:8080/api/customers/1

my server returns status code 200 and updates the data successfully. I searched through for a while but have no idea about this.