开玩笑模拟本地存储方法

Question

我想在玩笑中模拟 localStorage 方法以进行错误模拟。我在 utility.js 中定义了 localstorage getter 和 setter 方法。我想模拟

localStorage.setItem

在调用

utility.setItem

时抛出错误。

//file: utility.js
export default {
  getItem(key) {
    return localStorage.getItem(key);
  },
  setItem(key, value) {
    localStorage.setItem(key, value);
  }
};

开玩笑地说，

test('throw error', () => {
  localStorage.setItem = jest.fn(() => {
    console.log(" called ");
    throw new Error('ERROR');
  });

  utility.setItem('123', 'value');
});

但是

localStorage.setItem

mock永远不会被调用。我也尝试过做

window.localStorage.setItem = jest.genMockFunction(()=>{console.log(" Mock Called")});
global.localStorage.setItem = jest.fn(()=>{console.log(" Mock Called")});

Answer 1

jest.spyOn(window.localStorage.__proto__, 'setItem');

无需任何其他操作即可使用，如下所示：https://github.com/facebook/jest/issues/6798#issuecomment-440988627

Answer 2

这与 Andreas 在答案中的建议一致，但我能够使用 Storage 接口来模拟它。我做了这样的事情，

开玩笑地说，

test('throw error', () => {
  Storage.prototype.setItem = jest.fn(() => {
    console.log(" called "); // <-- was called 
    throw new Error('ERROR');
  });

  utility.setItem('123', 'value');
});

这个PR讨论也很有帮助。

Answer 3

如果你想测试 localStorage 功能，那么我建议使用 jest-localstorage-mock npm 包。

按照文档在安装测试文件中配置此包后，您就可以执行此操作。

test('should save to localStorage', () => {
  const KEY = 'foo',
    VALUE = 'bar';
  dispatch(action.update(KEY, VALUE));
  expect(localStorage.setItem).toHaveBeenLastCalledWith(KEY, VALUE);
  expect(localStorage.__STORE__[KEY]).toBe(VALUE);
  expect(Object.keys(localStorage.__STORE__).length).toBe(1);
});


test('should have cleared the sessionStorage', () => {
  dispatch(action.reset());
  expect(sessionStorage.clear).toHaveBeenCalledTimes(1);
  expect(sessionStorage.__STORE__).toEqual({}); // check store values
  expect(sessionStorage.length).toBe(0); // or check length
});

Answer 4

要访问被测模块全局范围内的内容，您需要使用

global

命名空间。因此，要访问

localStorage

，请使用

global.localStorage

:

global.storage = {
  store:{},
  getItem: (key)=>this.store[key],
  setItem: (key, value)=> this.store[key] = value
}

Answer 5

这里是 TS 版本 https://github.com/facebook/jest/issues/6798#issuecomment-440988627

import { afterAll, beforeAll } from '@jest/globals';

const mockWindowProperty = <P extends keyof Window>(property: P, value: Partial<Window[P]>) => {
  const { [property]: originalProperty } = window;
  delete window[property];
  beforeAll(() => {
    Object.defineProperty(window, property, {
      configurable: true,
      writable: true,
      value,
    });
  });
  afterAll(() => {
    window[property] = originalProperty;
  });
};

export default mockWindowProperty;