shallow的使用

```jsx
import { shallow } from 'enzyme'
let wrapper
beforeEach(() => {
wrapper = shallow()
})
```

PriceList是一个函数式组件
为什么wrapper的值是{}

Start with the shallow call and the PriceList component named in the issue, then inspect Enzyme's documented wrapper behavior and the component's props. Done means explaining why the observed value is {}, or documenting a reproducible behavior change with a focused test; no file or test path is provided.

Written by the indexing model from the issue text.