我正在尝试使用junit 5和mocking为我的SPRING-BOOT CRUD操作项目的控制器编写测试。运行测试时，显示以下错误。不明白是什么问题。
错误：-

10:24:51.840 [main] INFO org.springframework.test.web.servlet.TestDispatcherServlet -- Initializing Servlet ''
10:24:51.842 [main] INFO org.springframework.test.web.servlet.TestDispatcherServlet -- Completed initialization in 1 ms
10:24:51.865 [main] WARN org.springframework.web.servlet.PageNotFound -- No mapping for GET /content

java.lang.AssertionError: No value at JSON path "$.duration"

字符串
ContentController文件：-

package com.example.sixth.controller;

import com.example.sixth.entity.Content;
import com.example.sixth.service.ContentService;
import org.springframework.web.bind.annotation.*;

import java.util.List;
import java.util.Optional;

@RestController
public class ContentController {


    private final ContentService contentService;

    public ContentController(ContentService contentService) {
        this.contentService = contentService;
    }

    @GetMapping("/content")
    public List<Content> show(){
        return contentService.showAll();
    }

    @PostMapping("/content")
    public String save(@RequestBody Content content){
        return contentService.save(content);
    }

    @GetMapping("/content/title/{param}")
    public List<Content> getContentStartWith(@PathVariable("param") String title){
        return contentService.getContentStartWith(title);
    }

    @DeleteMapping("/content/{id}")
    public String delete(@PathVariable Integer id){
        return contentService.delete(id);
    }

    @GetMapping("/id")
    public List<Content>getById(@RequestParam Integer minId,
                                @RequestParam Integer maxId){
        return contentService.getById(minId,maxId);
    }

    @GetMapping("/content/{id}")
    public Optional<Content> findById(@PathVariable Integer id){
        return contentService.findById(id);
    }

}

型
测试文件：-

package com.example.sixth;

import com.example.sixth.controller.ContentController;
import com.example.sixth.entity.Content;
import com.example.sixth.service.ContentService;
import com.example.sixth.service.ContentServiceImpl;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.mockito.MockitoAnnotations;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.MockMvcBuilder;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
import org.springframework.test.web.servlet.result.MockMvcResultMatchers;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;
//import org.powermock.api.mockito.PowerMockito;

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

import static org.hamcrest.Matchers.is;
import static org.junit.jupiter.api.Assertions.assertEquals;

@AutoConfigureMockMvc
//@SpringBootTest
public class ContentControllerTest {

    @Autowired
    MockMvc mockMvc;

    @Mock
    ContentService mockService;

    @InjectMocks
    ContentController contentController;

    @BeforeEach
    public void init(){
        MockitoAnnotations.initMocks(this);

        this.mockMvc= MockMvcBuilders.standaloneSetup(mockService).build();
    }

    @Test
    public void testfindall() throws Exception {
        Content content = (Content.builder()
                .id(3)
                .title("SECOND!!")
                .duration(38)
                .location("Bangalore").build());
        List<Content> contentList = new ArrayList<>();
        contentList.add(content);
        Mockito.when(mockService.showAll()).thenReturn(contentList);
        
        mockMvc.perform(MockMvcRequestBuilders.get("/content").contentType(MediaType.APPLICATION_JSON)).andExpect(MockMvcResultMatchers.jsonPath("$.duration",is(content.getDuration())));
//        List<Content> actual=contentController.show();
//        System.out.println(actual.get(0).toString());
//        assertEquals(actual,contentList);

    }

型
顺便说一句，当使用assert时，它可以工作，但使用mockMvc时，它显示错误。