javascript - Jest 模拟 window.sessionStorage 的最佳方法是什么

Question

下面是一个非常简单的 Jest 单元测试，运行它时，你会得到这样的错误

Cannot spyOn on a primitive value; undefined given

TypeError: Cannot read property 'getItem' of undefined

但根据this post的最后两条评论, localStorage 和 sessionStorage 已经添加到最新的 JSDOM 和 jest 中。如果使用 jest-localstorage-mock并将它添加到我的 jest setupFiles 然后你会看到像

这样的奇怪错误

TypeError: object[methodName].mockImplementation is not a function

所以我的问题是 Jest 模拟 localStorage/sessionStorage 的最佳方式是什么。谢谢

describe('window.sessionStorage', () => {
    let mockSessionStorage;
    beforeEach(() => {
        mockSessionStorage = {};
        jest.spyOn(window.sessionStorage, "getItem").mockImplementation(key => {
            return mockSessionStorage[key];
        });
    });

    describe('getItem-', () => {
        beforeEach(() => {
            mockSessionStorage = {
                foo: 'bar',
            }
        });

        it('gets string item', () => {
            const ret = window.sessionStorage.getItem('foo');
            expect(ret).toBe('bar');
        });
    });
});

下面是我的jest配置

module.exports = {
    verbose: true,
    //setupFiles: ["jest-localstorage-mock"],
    testURL: "http://localhost/"
};

Answer 1

这里的解决方案只使用jestjs 和typescript，仅此而已。

index.ts:

export function getUserInfo() {
  const userInfo = window.sessionStorage.getItem('userInfo');
  if (userInfo) {
    return JSON.parse(userInfo);
  }
  return {};
}

index.spec.ts:

import { getUserInfo } from './';

const localStorageMock = (() => {
  let store = {};

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

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

describe('getUserInfo', () => {
  beforeEach(() => {
    window.sessionStorage.clear();
    jest.restoreAllMocks();
  });
  it('should get user info from session storage', () => {
    const getItemSpy = jest.spyOn(window.sessionStorage, 'getItem');
    window.sessionStorage.setItem('userInfo', JSON.stringify({ userId: 1, userEmail: 'example@gmail.com' }));
    const actualValue = getUserInfo();
    expect(actualValue).toEqual({ userId: 1, userEmail: 'example@gmail.com' });
    expect(getItemSpy).toBeCalledWith('userInfo');
  });

  it('should get empty object if no user info in session storage', () => {
    const getItemSpy = jest.spyOn(window.sessionStorage, 'getItem');
    const actualValue = getUserInfo();
    expect(actualValue).toEqual({});
    expect(window.sessionStorage.getItem).toBeCalledWith('userInfo');
    expect(getItemSpy).toBeCalledWith('userInfo');
  });
});

具有 100% 覆盖率报告的单元测试结果:

 PASS  src/stackoverflow/51566816/index.spec.ts
  getUserInfo
    ✓ should get user info from session storage (6ms)
    ✓ should get empty object if no user info in session storage (1ms)

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |      100 |      100 |      100 |      100 |                   |
 index.ts |      100 |      100 |      100 |      100 |                   |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        4.548s, estimated 6s

这是完整的演示:https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/51566816