unit-testing - 如何用 Jest 模拟导入

Question

我有一个像这样的小型 redux 中间件

import { hashHistory } from 'react-router'
import { REDIRECT_TO_LOGIN_REDIRECT_URL } from '../actions/login-redirect';
    
export default store => next => action => {
    
  if (action.type === REDIRECT_TO_LOGIN_REDIRECT_URL) {
    hashHistory.push(store.getState().loginRedirectUrl);
  }

  return next(action)
}

我现在想测试一下。正如您在第 1 行中看到的，我正在导入 hashHistory 并在稍后使用它。这是我要测试的(对 hashHistory 的调用)。为此，我必须模拟 hashHistory，但我不知道如何模拟。我正在使用 jest:

import { REDIRECT_TO_LOGIN_REDIRECT_URL } from '../actions/login-redirect';
import redirectMiddleware from './redirect-after-login';

describe('redirect after login middleware', () => {
    
  function setup() {
    const store = {
      subscribe: () => {},
      dispatch: () => {},
      getState: () => ({})
    };
    const next = jest.fn();
    const action = { type: REDIRECT_TO_LOGIN_REDIRECT_URL };
    return { store, next, action };
  }
        
  it('should push the redirect URL to the hashHistory', () => {
    // How to test it?
  })
    
});

Answer 1

你可以像这样模拟 react-router 模块:

import { hashHistory } from 'react-router'
import { REDIRECT_TO_LOGIN_REDIRECT_URL } from '../actions/login-redirect';
import redirectMiddleware from './redirect-after-login';
    
jest.mock('react-router', () => ({hashHistory: { push: jest.fn()}))

describe('redirect after login middleware', () => {  
  function setup() {
    const store = {
      subscribe: () => {},
      dispatch: () => {},
      getState: () => ({loginRedirectUrl: 'someLoginRedirectUrl'})
    };
    const next = jest.fn();
    const action = { type: REDIRECT_TO_LOGIN_REDIRECT_URL };
    return { store, next, action };
  }

  it('should push the redirect URL to the hashHistory', () => {
    const { store, next, action } = setup()
    redirectMiddleware(store)(next)(action)

    expect(hashHistory.push).toHaveBeenCalledWith('someLoginRedirectUrl')
  })
});