老师，您好，之前test.js 代码 按照课程上所述，如下

import React from 'react'
import { shallow } from 'enzyme'
import PriceList from '../PriceList'
import {items,categories} from '../../containers/Home'

const itemswithCategory = items.map((item) => {
    item.category = categories[item.categoryId];
    return item;
})
const props = {
    items: itemswithCategory,
    onEditItem: () => {},
    onDeleteItem: () => {},
}

let wrapper; 
describe('test PriceList component', () => {
    beforeEach(() => {
        wrapper = shallow(<PriceList {...props}/>)
    })
    it('should render the component to match snapshort',()=>{
        expect(wrapper).toMatchSnapshot()
    })
})

生成结果如下：　
//// Jest Snapshot v1, https://goo.gl/fbAQLP

//exports[test PriceList component should render the component to match snapshort 1] = ShallowWrapper {};

后来我查看了一下　自己的jest 版本和enzyme 版本。

-- react-scripts@3.0.1
  `-- jest@24.7.1
  `-- enzyme@3.10.0

发现可能是jest版本不匹配，过高。装了 https://github.com/adriantoine/enzyme-to-json

改变的代码如下

添加 import toJson from 'enzyme-to-json';
describe('test PriceList component', () => {
    beforeEach(() => {
        wrapper = shallow(<PriceList {...props}/>)
    })
    it('should render the component to match snapshort',()=>{
        expect(toJson(wrapper)).toMatchSnapshot()
    })
})

snapsot是有了。但是不知道这样tojson 会对快照有什么影响么。文档上说 Convert Enzyme wrappers to a format compatible with Jest snapshot testing.。。 为什么版本更新了反而需要compatible的东西了。
快照结果：

// Jest Snapshot v1, https://goo.gl/fbAQLP

exports[`test PriceList component should render the component to match snapshort 1`] = `
<ul
  className="list-group list-group-flush"
>
  <li
    className="list-group-item d-flex 
 justify-content-between align-items-center"
    key="1"
  >
    <span
      className="col-1"
    >
      <Ionicon
        beat={false}
        color="#6BE61A"
        fontSize="30px"
        icon="md-restaurant"
        rotate={false}
        shake={false}
        style={
          Object {
            "backgroundColor": "#347eff",
            "padding": "5px",
          }
        }
      />
    </span>
    <span
      className="col-5"
    >
      testItem
    </span>
    <span
      className="col-2 font-weight-bold"
    >
      -
       
      200
    </span>
    <span
      className="col-2"
    >
      2018-09-10
    </span>
    <a
      className="col-1"
      onClick={[Function]}
      role="button"
      style={
        Object {
          "cursor": "pointer",
        }
      }
    >
      <Ionicon
        beat={false}
        color="#6BE61A"
        fontSize="20px"
        icon="md-create"
        rotate={false}
        shake={false}
        style={Object {}}
      />
    </a>
    <a
      className="col-1"
      onClick={[Function]}
      role="button"
      style={
        Object {
          "cursor": "pointer",
        }
      }
    >
      <Ionicon
        beat={false}
        color="#6BE61A"
        fontSize="20px"
        icon="md-trash"
        rotate={false}
        shake={false}
        style={Object {}}
      />
    </a>
  </li>
  <li
    className="list-group-item d-flex 
 justify-content-between align-items-center"
    key="2"
  >
    <span
      className="col-1"
    >
      <Ionicon
        beat={false}
        color="#6BE61A"
        fontSize="30px"
        icon="md-train"
        rotate={false}
        shake={false}
        style={
          Object {
            "backgroundColor": "#347eff",
            "padding": "5px",
          }
        }
      />
    </span>
    <span
      className="col-5"
    >
      testItem2
    </span>
    <span
      className="col-2 font-weight-bold"
    >
      +
       
      300
    </span>
    <span
      className="col-2"
    >
      2018-09-10
    </span>
    <a
      className="col-1"
      onClick={[Function]}
      role="button"
      style={
        Object {
          "cursor": "pointer",
        }
      }
    >
      <Ionicon
        beat={false}
        color="#6BE61A"
        fontSize="20px"
        icon="md-create"
        rotate={false}
        shake={false}
        style={Object {}}
      />
    </a>
    <a
      className="col-1"
      onClick={[Function]}
      role="button"
      style={
        Object {
          "cursor": "pointer",
        }
      }
    >
      <Ionicon
        beat={false}
        color="#6BE61A"
        fontSize="20px"
        icon="md-trash"
        rotate={false}
        shake={false}
        style={Object {}}
      />
    </a>
  </li>
</ul>
`;