Let's quickly write a unit test checking for the JSON response and then add the test to BasicControllerTest:

    @Test
    fun `GET welcome-with-object returns "Hello World"`() {
      mvc.perform(MockMvcRequestBuilders.get("/welcome-with-object")
                                        .accept(MediaType.APPLICATION_JSON))
         .andExpect(status().isOk())
         .andExpect(content().string(containsString("Hello World")));
    }

This test is very similar to the earlier unit test, except that we are using containsString to check whether the content contains a "Hello World" substring.