jest.fn()如何工作 [英] How does jest.fn() work

问题描述

任何人都可以解释jest.fn()在实际示例中的实际工作方式，因为我对如何使用它以及必须在何处使用感到困惑.

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

例如，如果我具有在实用工具"功能的帮助下单击按钮即可获取国家/地区列表的国家/地区

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>
    );

  }
}

使用的实用程序功能

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));
        });
      });


    }

当我单击按钮时，我可以在哪里使用Jest.fn()或如何测试getList函数的调用

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

推荐答案

笑话功能

模拟功能也被称为间谍"，因为它们使您可以监视被其他代码间接调用的功能的行为，而不仅仅是测试输出.您可以使用jest.fn()创建模拟函数.

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().

检查文档中的jest.fn()

返回一个新的未使用的模拟函数. (可选)采用模拟实现.

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

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

通过模拟实现:

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

---

因此，您可以使用jest.fn()来模拟getList，如下所示:

---

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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