Why does MockMvc always return empty content()?

Question

I'm trying to test my rest api with mockMvc.

mockMvc.perform(get("/users/1/mobile")
        .accept(MediaType.APPLICATION_JSON))
        .andExpect(status().isOk())
        .andDo(print())
        .andExpect(content().string("iPhone"))

The test failed because of:

java.lang.AssertionError: Response content 
Expected :iPhone
Actual   :

From the output of print(), I can know the API actually returned the expected string "iPhone".

ModelAndView:
        View name = users/1/mobile
             View = null
        Attribute = treeNode
            value = "iPhone"
           errors = []

And I guess the empty "Actual" above is caused by empty "Body" below

MockHttpServletResponse:
           Status = 200
    Error message = null
          Headers = {}
     Content type = null
             Body = 
    Forwarded URL = users/1/mobile
   Redirected URL = null
          Cookies = []

My questions are:

Why MockHttpServletResponse's Body is empty;
How can I correctly test the response of API.

Please add the controller you're testing (the Subject Under Test) — Ali Dehghani
– Ali Dehghani, Commented Oct 16, 2016 at 7:43

knittl · Accepted Answer · 2022-02-07 19:52:33Z

6

If your action methods (methods with @RequestMapping annotation) return instances of ModelAndView or you work with Model, you have to test it using MockMvcResultMatchers#model function:

.andExpect(MockMvcResultMatchers.model().attribute("phone", "iPhone"))
.andExpect(MockMvcResultMatchers.model().size(1))

MockMvcResultMatchers#content is appropriate for REST action methods (methods with @RequestBody annotation).

To have a better understanding about testing Spring MVC and Spring REST controllers check these links:

edited Feb 7, 2022 at 19:52

knittl

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answered Oct 16, 2016 at 19:23

Anton Dozortsev

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1 Comment

RASMiranda Over a year ago

but those are just the attributes of the model, is there any way to test the view render?

marcello · Accepted Answer · 2019-11-29 20:14:24Z

6

Just adding another reason for this error, that took me a whole day to discover. I successfully created an APITest using mockito and mockmvc class, using the perform method. Then copied the code to produce another service and I started to get an empty body over and over again.

Nonetheless, at the end of the day I decided to compare each copied class from one project to another. The only one difference that I found was the @EqualsAndHashCode annotation in my request DTO that is received by the new controller.

So, the recommendation is: add the @EqualsAndHashCode annotation in your DTO classes.

edited Nov 29, 2019 at 20:14

answered Jul 7, 2019 at 2:57

marcello

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2 Comments

Mahdi Shabani Over a year ago

That is the true answer. Great...

user10613856 Over a year ago

Amazing. This really did the trick for me! Thank you.

Kxrr · Accepted Answer · 2025-04-22 07:26:33Z

0

In a testing scenario, a common issue arises when using mocking frameworks like Mockito to mock Spring Filters/Interceptors. If the filter.proceed() method isn't invoked or returns null, the subsequent web response logic isn't executed, resulting in an empty response body.

answered Apr 22 at 7:26

Kxrr

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