NodeJS环境下无法Mock ES6导入函数的问题求助

我尝试Mock导入的fetchLiveMatches函数已有一段时间，但始终未成功。查阅相关资料后仍无头绪，希望获得帮助。以下是我的代码及错误信息，请问我哪里出错了？

live.test.js #

import * as liveController from "./live";
import { jest } from "@jest/globals";
import * as liveService from "../service/live";
import { buildReq, buildRes, buildNext } from "../utils/testingHelper";

jest.mock("../service/live");

beforeEach(() => {
  jest.clearAllMocks();
});

describe("Live Controller", () => {
  test("calls fetchLiveMatches function to fetch from external API", async () => {
    const req = buildReq();
    const res = buildRes();
    const next = buildNext();

    await liveController.getLiveMatches(req, res, next);

    expect(next).not.toHaveBeenCalled();
    expect(liveService.fetchLiveMatches).toHaveBeenCalled();
    expect(res.status).toHaveBeenCalledWith(500);
    expect(res.status).toHaveBeenCalledTimes(1);
  });
});

service/live.js #

import axios from "axios";

async function fetchLiveMatches() {
  // Some hidden code

  return axios({
    method: "get",
    url: `${API_FOOTBALL_BASE_URL}${GET_EVENTS}${MATCH_LIVE}${WIDGET_KEY}${TIMEZONE}${DETAILS}`,
    headers: {}
  }).then(res => res.data);
}

export { fetchLiveMatches };

jest.config.js #

export default {
  testEnvironment: "jest-environment-node",
  transform: {}
};

package.json #

{
  "name": "server",
  "version": "1.0.0",
  "main": "index.js",
  "type": "module",
  "license": "MIT",
  "dependencies": {
    "express": "^4.18.2"
  },
  "devDependencies": {
    "axios": "^1.1.3",
    "eslint": "^8.26.0",
    "jest": "^29.2.2",
    "prettier": "^2.7.1"
  },
  "scripts": {
    "start": "node --watch index.js",
    "start:no-watch": "node index.js",
    "test": "node --experimental-vm-modules node_modules/jest/bin/jest.js --watch"
  }
}

测试错误输出 #

Live Controller › calls fetchLiveMatches function to fetch from external API
                                                                                 
    expect(received).toHaveBeenCalled()                                           
                                                                                 
    Matcher error: received value must be a mock or spy function                 
                                                                                 
    Received has type:  function
    Received has value: [Function fetchLiveMatches]

问题根源是你的项目使用ES模块（package.json中type: module），Jest的jest.mock()自动mock逻辑在ES模块环境下无法直接将导出函数替换为mock函数，导致你调用的还是原函数而非mock。

修复方案一：手动替换为mock函数 #

直接在测试文件中将fetchLiveMatches替换为Jest mock函数：

import * as liveController from "./live";
import { jest } from "@jest/globals";
import * as liveService from "../service/live";
import { buildReq, buildRes, buildNext } from "../utils/testingHelper";

// 手动将原函数替换为mock
liveService.fetchLiveMatches = jest.fn();

beforeEach(() => {
  jest.clearAllMocks();
});

describe("Live Controller", () => {
  test("calls fetchLiveMatches function to fetch from external API", async () => {
    const req = buildReq();
    const res = buildRes();
    const next = buildNext();

    // 可选：如果需要触发res.status(500)，让mock函数抛出错误
    liveService.fetchLiveMatches.mockRejectedValue(new Error('API请求失败'));

    await liveController.getLiveMatches(req, res, next);

    expect(next).not.toHaveBeenCalled();
    expect(liveService.fetchLiveMatches).toHaveBeenCalled();
    expect(res.status).toHaveBeenCalledWith(500);
    expect(res.status).toHaveBeenCalledTimes(1);
  });
});

修复方案二：使用Jest mock目录 #

通过创建__mocks__目录来实现自动mock：

1. 在service目录下新建__mocks__/live.js文件：

export const fetchLiveMatches = jest.fn();

2. 修改jest.config.js，添加ES模块兼容配置：

export default {
  testEnvironment: "jest-environment-node",
  transform: {},
  esModuleInterop: true,
  moduleNameMapper: {
    "^../service/live$": "<rootDir>/service/__mocks__/live.js"
  }
};

3. 测试文件中保留jest.mock("../service/live");即可，此时Jest会自动加载mock目录中的函数。

内容的提问来源于stack exchange，提问作者tiagoornelas