使用Jest、Supertest、MongoDB与Express测试Express路由时遭遇环境销毁错误的求助

我在使用Jest和Supertest测试Express路由时碰到了棘手的问题：启动应用时我会连接MongoDB并把MongoClient存入app.locals，但一加上这个连接逻辑就会报错；注释掉连接调用后，错误消失但会收到Jest的未退出警告。

报错信息 #

ReferenceError: You are trying to `import` a file after the Jest environment has been torn down.
at BufferList.Readable (server/node_modules/readable-stream/lib/_stream_readable.js:179:22)
at BufferList.Duplex (server/node_modules/readable-stream/lib/_stream_duplex.js:67:12)
at new BufferList (server/node_modules/bl/bl.js:33:16)
at new MessageStream (server/node_modules/mongodb/lib/cmap/message_stream.js:35:21)
at new Connection (server/node_modules/mongodb/lib/cmap/connection.js:54:28)
/Users/zackchan/Documents/dev/server/node_modules/readable-stream/lib/_stream_readable.js:111
var isDuplex = stream instanceof Duplex;
^
TypeError: Right-hand side of 'instanceof' is not callable
at new ReadableState (/Users/zackchan/Documents/dev/server/node_modules/readable-stream/lib/_stream_readable.js:111:25)
at BufferList.Readable (/Users/zackchan/Documents/dev/server/node_modules/readable-stream/lib/_stream_readable.js:183:25)
at BufferList.Duplex (/Users/zackchan/Documents/dev/server/node_modules/readable-stream/lib/_stream_duplex.js:67:12)
at new BufferList (/Users/zackchan/Documents/dev/server/node_modules/bl/bl.js:33:16)
at new MessageStream (/Users/zackchan/Documents/dev/server/node_modules/mongodb/lib/cmap/message_stream.js:35:21)
at new Connection (/Users/zackchan/Documents/dev/server/node_modules/mongodb/lib/cmap/connection.js:54:28)
at /Users/zackchan/Documents/dev/server/node_modules/mongodb/lib/core/connection/connect.js:36:29
at callback (/Users/zackchan/Documents/dev/server/node_modules/mongodb/lib/core/connection/connect.js:280:5)
at TLSSocket.connectHandler (/Users/zackchan/Documents/dev/server/node_modules/mongodb/lib/core/connection/connect.js:325:5)
at Object.onceWrapper (events.js:421:28)

注释MongoDB连接后的警告 #

Jest did not exit one second after the test run has completed. This usually means that there are asynchronous operations that weren't stopped in your tests. Consider running Jest with --detectOpenHandles to troubleshoot this issue.

相关代码 #

app.js

const https = require('https');
const fs = require('fs');
const path = require('path');
const dotenv = require('dotenv');
const express = require('express');
const rateLimiter = require('express-rate-limit');
const { MongoClient } = require('mongodb');

const app = express();
const port = process.env.PORT || 443;

const limit = rateLimiter({
  window: 15 * 60 * 1000,
  max: 100
});

var httpsOptions;
if(process.env.NODE_ENV === 'development'){
  const rootCA = require('ssl-root-cas').create().addFile(path.join(__dirname, './cert/CA.pem'));
  https.globalAgent.options.ca = rootCA;
  httpsOptions = {
    key: fs.readFileSync(path.join(__dirname, './cert/localhost.key')),
    cert: fs.readFileSync(path.join(__dirname, './cert/localhost.crt'))
  };
}

MongoClient.connect(process.env.MONGODB_URI, { useNewUrlParser: true, useUnifiedTopology: true }, (err, mongoClient) => {
  if(err) throw err;
  app.locals.mongoClient = mongoClient;
});

app.use(limit);
app.use(express.json());

app.get('/', (req, res) => {
  res.json({path: '/'});
});

const server = https.createServer(httpsOptions, app).listen(port);

module.exports = app;

test.js

const dotenv = require('dotenv');
const path = require('path');
process.env = dotenv.config({path: path.resolve(__dirname, '.env')}).parsed;

const request = require('supertest');
const app = require('../app');

describe('GET /', () => {
  it('responds with path of /', (done) => {
    // app.locals is empty here
    request(app).get('/').expect(JSON.stringify({path: '/'}), done);
  });
});

我试过在测试结束后调用app.locals.mongoClient.close()，但这里mongoClient是undefined；也试过把MongoClient.connect()包在async函数里执行，都没效果。求可行的解决思路！

我之前碰到过几乎一模一样的问题，核心就是异步连接和测试生命周期没有对齐，下面几个方案亲测有效：

1. 重构App的MongoDB连接逻辑，改为异步导出 #

当前你的MongoClient.connect是异步执行的，但你直接同步导出了app，导致测试启动时连接还没建立（所以app.locals.mongoClient是undefined），而且Jest跑完测试后连接还在后台运行，引发环境销毁错误。

修改app.js，把连接逻辑改成Promise风格，导出一个能获取已连接app的函数：

// app.js 改造后
const https = require('https');
const fs = require('fs');
const path = require('path');
const dotenv = require('dotenv');
const express = require('express');
const rateLimiter = require('express-rate-limit');
const { MongoClient } = require('mongodb');

dotenv.config(); // 这里直接加载env，不用在测试里重复处理

const createApp = async () => {
  const app = express();
  const port = process.env.PORT || 443;

  const limit = rateLimiter({
    window: 15 * 60 * 1000,
    max: 100
  });

  var httpsOptions;
  if(process.env.NODE_ENV === 'development'){
    const rootCA = require('ssl-root-cas').create().addFile(path.join(__dirname, './cert/CA.pem'));
    https.globalAgent.options.ca = rootCA;
    httpsOptions = {
      key: fs.readFileSync(path.join(__dirname, './cert/localhost.key')),
      cert: fs.readFileSync(path.join(__dirname, './cert/localhost.crt'))
    };
  }

  // 异步等待MongoDB连接完成
  const mongoClient = await MongoClient.connect(process.env.MONGODB_URI, { 
    useNewUrlParser: true, 
    useUnifiedTopology: true 
  });
  app.locals.mongoClient = mongoClient;

  app.use(limit);
  app.use(express.json());

  app.get('/', (req, res) => {
    res.json({path: '/'});
  });

  // 只有非测试环境才启动HTTP服务，测试时由Supertest处理
  if (process.env.NODE_ENV !== 'test') {
    https.createServer(httpsOptions, app).listen(port);
  }

  return app;
};

module.exports = createApp;

2. 修改测试用例，对齐测试生命周期 #

现在测试需要调用createApp()来获取已连接好的app，并且在测试套件结束后主动关闭MongoDB连接：

// test.js 改造后
const dotenv = require('dotenv');
const path = require('path');
dotenv.config({path: path.resolve(__dirname, '.env')}); // 直接加载env即可

const request = require('supertest');
const createApp = require('../app');

describe('GET /', () => {
  let app;
  let mongoClient;

  // 所有测试前初始化App和连接
  beforeAll(async () => {
    app = await createApp();
    mongoClient = app.locals.mongoClient;
  });

  // 所有测试后关闭连接
  afterAll(async () => {
    await mongoClient.close();
  });

  it('responds with path of /', async () => {
    const response = await request(app).get('/');
    expect(response.text).toBe(JSON.stringify({path: '/'}));
  });
});

3. 可选优化：全局统一管理连接（多测试文件场景） #

如果你的测试用例很多，不想每个测试文件都写一遍连接逻辑，可以用Jest的全局Setup/Teardown：

• 项目根目录创建jest.setup.js：

const createApp = require('./server/app'); // 对应你的app路径
global.app = null;
global.mongoClient = null;

beforeAll(async () => {
  global.app = await createApp();
  global.mongoClient = global.app.locals.mongoClient;
});

afterAll(async () => {
  await global.mongoClient.close();
});

• 在jest.config.js里添加配置：

module.exports = {
  setupFilesAfterEnv: ['./jest.setup.js'],
};

这样所有测试文件都能直接使用global.app，不用重复初始化。

4. 关于“Jest did not exit...”警告 #

这个警告本质是测试结束后还有未关闭的异步资源（MongoDB连接、HTTP服务器），上面的方案里：

• afterAll主动关闭MongoDB连接
• createApp里只在非测试环境启动HTTP服务器，避免额外资源占用
  两者结合就能彻底解决这个警告。

内容的提问来源于stack exchange，提问作者Zack