@RunWith(SpringRunner.class)
@SpringBootTest
public class UserControllerTest {
}

 // 注入Spring 工厂
  @Autowired
  private WebApplicationContext wac;
 //伪造mvc环境
  private MockMvc mockMvc;
  @Before
  public void setup(){
    mockMvc = MockMvcBuilders.webAppContextSetup(wac).build();
  }

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.put;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.delete;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@Test
  public void whenXXXXSuccess() throws Exception {
    //模拟发送请求
    String result =
    mockMvc.perform(get("/user") //发往/user的get请求,可以换成post，put，delete方法执行相应请求
            .param("username","xxx") //get请求时填写参数的位置
            .contentType(MediaType.APPLICATION_JSON_UTF8) //utf编码
            .content(content)) //post和put请求填写参数的位置
        .andExpect(status().isOk())
        .andExpect(jsonPath("$.length()").value(3)) //期望的json返回结果
        .andReturn().getResponse().getContentAsString(); //对返回字符串的json内容进行判断
    log.info(result);
  }