jest.fn() 有什么作用，我该如何使用它? [英] What does jest.fn() do and how can I use it?

问题描述

谁能用一个真实世界的例子来解释 jest.fn() 实际上是如何工作的，因为我对如何使用它以及必须在哪里使用它感到困惑.

例如，如果我有一个组件 Country，它可以在 Utils 功能的帮助下单击按钮获取国家列表

export default class countries extends React.Component {构造函数(道具){超级(道具)this.state = {国家列表:''}}获取列表(){//e.preventDefault();//在这里做一个api调用让列表 = getCountryList();list.then((response)=>{ this.setState({ countryList:response }) });}使成为() {var cListing = "单击按钮加载国家列表";如果(this.state.countryList){让 cList = JSON.parse(this.state.countryList);cListing = cList.RestResponse.result.map((item)=> { return(
 {item.name} 
); });}返回 (<div><button onClick={()=>this.getList()} className=buttonStyle">显示国家列表 </button><ul>{cListing}

);}}

使用的Utils函数

const http = require('http');导出函数 getCountryList() {返回新的承诺(解决 => {让 url = "/country/get/all";http.get({host:'services.groupkt.com',path: url,withCredentials:false}, response => {让数据 = '';response.on('data', _data => data += _data);response.on('end', () => resolve(data));});});}

我可以在哪里使用 Jest.fn() 或者我如何测试当我点击按钮时调用 getList 函数

解决方案

Jest Mock 函数

模拟函数也被称为间谍"，因为它们让您可以监视由其他代码间接调用的函数的行为，而不仅仅是测试输出.您可以使用 jest.fn() 创建一个模拟函数.

检查 jest.fn() 的文档

返回一个新的、未使用的模拟函数.可选地采用模拟实现.

 const mockFn = jest.fn();模拟Fn();期望(mockFn).toHaveBeenCalled();

使用模拟实现:

 const returnsTrue = jest.fn(() => true);console.log(returnsTrue())//true;

---

所以你可以使用 jest.fn() 模拟 getList 如下:

jest.dontMock('./Countries.jsx');const React = require('react/addons');const TestUtils = React.addons.TestUtils;const Country = require('./Countries.jsx');描述('组件'，函数(){it('必须在点击按钮时调用 getList', function() {var renderNode = TestUtils.renderIntoDocument();renderNode.prototype.getList = jest.fn()var button = TestUtils.findRenderedDOMComponentWithTag(renderedNode, 'button');TestUtils.Simulate.click(button);期望(renderedNode.prototype.getList).toBeCalled();});});

Can anyone explain how jest.fn() actually works, with a real world example, as I'm confused on how to use it and where it has to be used.

For example if I have the component Countries which fetches country List on click of a button with help of the Utils Function

export default class Countries extends React.Component {
  constructor(props) {
    super(props)

    this.state = {
      countryList:''
    }
  }

  getList() {
    //e.preventDefault();
    //do an api call here
    let list = getCountryList();
    list.then((response)=>{ this.setState({ countryList:response }) });
  }

  render() {

    var cListing = "Click button to load Countries List";

    if(this.state.countryList) {
      let cList = JSON.parse(this.state.countryList);
      cListing = cList.RestResponse.result.map((item)=> { return(<li key={item.alpha3_code}> {item.name} </li>); });
    }

    return (
      <div>
        <button onClick={()=>this.getList()} className="buttonStyle"> Show Countries List </button>
        <ul>
          {cListing}
        </ul>
      </div>
    );

  }
}

Utils function used

const http = require('http');


    export function getCountryList() {
      return new Promise(resolve => {
        let url = "/country/get/all";
        http.get({host:'services.groupkt.com',path: url,withCredentials:false}, response => {
          let data = '';
          response.on('data', _data => data += _data);
          response.on('end', () => resolve(data));
        });
      });
    
    
    }

where could i use Jest.fn() or how can i test for getList function is called when i click on the Button

解决方案

Jest Mock Functions

Mock functions are also known as "spies", because they let you spy on the behavior of a function that is called indirectly by some other code, rather than just testing the output. You can create a mock function with jest.fn().

Check the documentation for jest.fn()

Returns a new, unused mock function. Optionally takes a mock implementation.

  const mockFn = jest.fn();
  mockFn();
  expect(mockFn).toHaveBeenCalled();

With a mock implementation:

  const returnsTrue = jest.fn(() => true);
  console.log(returnsTrue()) // true;

---

So you can mock getList using jest.fn() as follows:

jest.dontMock('./Countries.jsx');
const React = require('react/addons');
const TestUtils = React.addons.TestUtils;
const Countries = require('./Countries.jsx');

describe('Component', function() {
  it('must call getList on button click', function() {
    var renderedNode = TestUtils.renderIntoDocument(<Countries />);
    renderedNode.prototype.getList = jest.fn()

    var button = TestUtils.findRenderedDOMComponentWithTag(renderedNode, 'button');

    TestUtils.Simulate.click(button);

    expect(renderedNode.prototype.getList).toBeCalled();
  });
});

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