Jest测试时node_modules模块导入报undefined，求排查配置问题

问题重现 #

执行Jest测试时，所有从node_modules导入的模块均返回undefined，示例测试代码如下：

import lodash from 'lodash'

it('test', () => {
  expect(lodash.max([1,2])).toBe(2)
})

测试抛出错误：

Cannot read properties of undefined (reading 'max')
TypeError: Cannot read properties of undefined (reading 'max')

相关配置文件：

jest.config.js #

/** @type {import('ts-jest').JestConfigWithTsJest} */
const tsconfig = require('./tsconfig.json')
const moduleNameMapper = require('tsconfig-paths-jest')(tsconfig)

module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'node',
  moduleNameMapper,
}

webpack.config.js #

const path = require('path')
const TsconfigPathsPlugin = require('tsconfig-paths-webpack-plugin').default
const nodeExternals = require('webpack-node-externals')

module.exports = {
  entry: './src/server.ts',
  target: 'node',
  externals: [nodeExternals()],
  devtool: 'source-map',
  mode: process.env.RUNTIME_ENV === 'production' ? 'production' : 'development',
  module: {
    rules: [
      {
        test: /\.(ts|js)$/,
        use: 'ts-loader',
        exclude: /node_modules/,
      },
      {
        test: /\.(graphql|gql)$/,
        loader: '@graphql-tools/webpack-loader',
      },
    ],
  },
  resolve: {
    extensions: ['.tsx', '.ts', '.js'],
    plugins: [new TsconfigPathsPlugin({})],
  },
  output: {
    filename: '[name].js',
    path: path.resolve(__dirname, 'dist'),
  },
}

tsconfig.json #

{
  "compilerOptions": {
    "lib": ["ESNext"],
    "moduleResolution": "node",
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "removeComments": true,
    "sourceMap": true,
    "target": "ES2020",
    "outDir": "lib",
    "isolatedModules": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "resolveJsonModule": true,
    "baseUrl": ".",
    "allowJs": true,
    "allowSyntheticDefaultImports": true
  },
  "include": ["src/**/*.ts","./global.d.ts"],
  "exclude": [
    "node_modules/**/*",
    "_warmup/**/*",
    ".vscode/**/*"
  ]
}

问题原因 #

核心问题是tsconfig-paths-jest生成的moduleNameMapper完全覆盖了Jest默认的模块解析规则，导致Jest无法正确识别并加载node_modules中的第三方模块。

解决办法 #

1. 修复jest.config.js的moduleNameMapper配置 #

不要直接将tsconfig-paths-jest的返回值赋值给moduleNameMapper，而是将其合并到Jest的默认配置中，保留Jest对node_modules的解析逻辑：

/** @type {import('ts-jest').JestConfigWithTsJest} */
const tsconfig = require('./tsconfig.json')
const pathsMapper = require('tsconfig-paths-jest')(tsconfig)

module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'node',
  // 合并路径别名映射，保留Jest默认模块解析规则
  moduleNameMapper: {
    ...pathsMapper,
  },
}

2. 验证依赖完整性 #

确保已安装必要的开发依赖：

npm install --save-dev ts-jest typescript @types/jest @types/lodash

3. 重新运行测试 #

修改配置后，重新执行Jest测试，此时应该能正确解析lodash等第三方模块，测试正常运行。

内容的提问来源于stack exchange，提问作者zibra