2022年12月:Nx 14使用Angular 14 Jest。 我们有一个测试设置。Ts文件在每个app和libs文件夹。我们设置本地存储模拟全局。

import 'jest-preset-angular/setup-jest';

Storage.prototype.getItem = jest.fn();
Storage.prototype.setItem = jest.fn();
Storage.prototype.removeItem = jest.fn();

然后localStorage.service.spec.ts文件如下所示:

import { LocalStorageService } from './localstorage.service';

describe('LocalStorageService', () => {
    let localStorageService: LocalStorageService;

    beforeEach(() => {
        localStorageService = new LocalStorageService();
    });

    it('should set "identityKey" in localStorage', async () => {
        localStorageService.saveData('identityKey', '99');
        expect(window.localStorage.setItem).toHaveBeenCalled();
 expect(window.localStorage.setItem).toHaveBeenCalledWith('identityKey', '99');
        expect(window.localStorage.setItem).toHaveBeenCalledTimes(1);
});

it('should get "identityKey" from localStorage', async () => {
    localStorageService.getData('identityKey');
    expect(window.localStorage.getItem).toHaveBeenCalled();
    expect(window.localStorage.getItem).toHaveBeenCalledWith('identityKey');
    expect(window.localStorage.getItem).toHaveBeenCalledTimes(1);
});

it('should remove "identityKey" from localStorage', async () => {
    localStorageService.removeData('identityKey');
    expect(window.localStorage.removeItem).toHaveBeenCalled();
expect(window.localStorage.removeItem).toHaveBeenCalledWith('identityKey');
            expect(window.localStorage.removeItem).toHaveBeenCalledTimes(1);
        });
    });

注:不好意思，这个SatckOverflow窗口很糟糕。

正如Niket Pathak在评论中提到的， 从jest@24 / jsdom@11.12.0及以上开始，localStorage将自动被模拟。

我从github找到了这个解决方案

var localStorageMock = (function() {
  var store = {};

  return {
    getItem: function(key) {
        return store[key] || null;
    },
    setItem: function(key, value) {
        store[key] = value.toString();
    },
    clear: function() {
        store = {};
    }
  }; 
})();

Object.defineProperty(window, 'localStorage', {
 value: localStorageMock
});

您可以在setupTests中插入这段代码，它应该可以正常工作。

我在一个使用typesctipt的项目中测试了它。

不需要模拟localStorage—只需使用jsdom环境，这样您的测试就可以在类似浏览器的条件下运行。

在你的joke。config。js中，

module.exports = {
    // ...
    testEnvironment: "jsdom"
}
    

答:

目前(7月22日)localStorage不能像你通常会被嘲笑或监视，并在创建-反应-应用程序文档中概述。这是由于jsdom中所做的更改。你可以在jest和jsdom问题跟踪器中读到它。

作为一种变通方法，你可以监视原型:

// does not work:
jest.spyOn(localStorage, "setItem");
localStorage.setItem = jest.fn();

// either of these lines will work, different syntax that does the same thing:
jest.spyOn(Storage.prototype, 'setItem');
Storage.prototype.setItem = jest.fn();

// assertions as usual:
expect(localStorage.setItem).toHaveBeenCalled();

关于监视原型机的注意事项:

监视实例使您能够观察和模拟特定对象的行为。

另一方面，监视原型，将同时观察/操作该类的每个实例。除非您有一个特殊的用例，否则这可能不是您想要的。

但是，在本例中没有区别，因为localStorage只存在一个实例。

对于Jest, React和TypeScript用户:

我创建了一个mockLocalStorage.ts

export const mockLocalStorage = () => {
  const setItemMock = jest.fn();
  const getItemMock = jest.fn();

  beforeEach(() => {
    Storage.prototype.setItem = setItemMock;
    Storage.prototype.getItem = getItemMock;
  });

  afterEach(() => {
    setItemMock.mockRestore();
    getItemMock.mockRestore();
  });

  return { setItemMock, getItemMock };
};

我的组件:

export const Component = () => {
    const foo = localStorage.getItem('foo')
    localStorage.setItem('bar', 'true')
    return <h1>{foo}</h1>
}

然后在我的测试中，我这样使用它:

import React from 'react';

import { mockLocalStorage } from '../../test-utils';
import { Component } from './Component';

const { getItemMock, setItemMock } = mockLocalStorage();

it('fetches something from localStorage', () => {
    getItemMock.mockReturnValue('bar');
    render(<Component />);
    expect(getItemMock).toHaveBeenCalled();
    expect(getByText(/bar/i)).toBeInTheDocument()
});

it('expects something to be set in localStorage' () => {
    const value = "true"
    const key = "bar"
    render(<Component />);
    expect(setItemMock).toHaveBeenCalledWith(key, value);
}