如何嘲笑Picker和Picker.Item with jest in React-Native

Question

我正在尝试快照测试这段代码:

import React, { Component } from 'react';
import {
  Picker,
} from 'react-native';
export default class TestComponent extends Component {
  render() {
    return (
      <Picker
        selectedValue={this.props.asset.type}
        onValueChange={this.props.onTypeChange}>
        <Picker.Item label="Type of asset" value="default" />
        <Picker.Item label="Car" value="car" />
        <Picker.Item label="Boat" value="boat" />
        <Picker.Item label="Ship" value="ship" />
      </Picker>
    );
  }
}

我的测试现在是这样的:

import 'react-native';
import React from 'react';
import TestComponent from './TestComponent';
import renderer from 'react-test-renderer';
describe('TestComponent', () => {
  const asset = {
    type: 'car',
  }
  it('renders correctly', () => {
    const tree = renderer.create(
      <TestComponent 
        asset={asset} />
    ).toJSON();
    expect(tree).toMatchSnapshot();
  });
})

我的问题是我得到:

TypeError: Cannot read property '_tag' of undefined

基于这个问题，我认为我应该嘲笑它

我试过简单地添加:

jest.mock('Picker', () => 'Picker')

但是它仍然抛出一个错误，因为Picker。项目仍未被模拟

Invariant Violation: Element type is invalid: expected a string (for built-
in components) or a class/function (for composite components) 
but got: undefined. Check the render method of `TestComponent`.

我尝试了其他没有效果的变体:

jest.mock('Picker', () => {return {Item: 'Item'}});
----------------------------------------------------
class Picker{
  Item = 'PickerItem'
}
jest.mock('Picker', () => {
  return Picker;
});

Answer 1

创建了一个github问题，这里是一个工作的答案:

jest.mock('Picker', () => {
  const Picker = class extends Component {
    static Item = props => React.createElement('Item', props, props.children);
    static propTypes = { children: React.PropTypes.any };
    render() {
      return React.createElement('Picker', this.props, this.props.children);
    }
  }
  return Picker;
})

Answer 2

对于Expo v39，我可以通过在测试/设置文件中添加以下模拟来测试@react-native-community/picker:

jest.mock('@react-native-community/picker', () => {
  const React = require('React')
  const RealComponent = jest.requireActual('@react-native-community/picker')
  class Picker extends React.Component {
    static Item = (props: { children: never }) => {
      return React.createElement('Item', props, props.children)
    }
    render () {
      return React.createElement('Picker', this.props, this.props.children)
    }
  }
  Picker.propTypes = RealComponent.propTypes
  return {
    Picker
  }
})

注意@react-native-community/picker现在是react-native-picker/picker。

https://jestjs.io/docs/en/tutorial-react-native提示