DNSCHANNEL stops jest from closing

[presentsvlad]

Jest does not closed himself after test finished

--detectOpenHandles suggest I need to close DNSCHANNEL manually:

Jest has detected the following 1 open handle potentially keeping Jest from exiting:

  ●  DNSCHANNEL

      at dns.js:333:23

But I cannot find any additonal information based on that problem.

I have async tests running supertest and jest.

    "express": "^4.16.3",
    "jest": "^23.1.0",
    "supertest": "^3.1.0",
    "pg": "^7.4.3",
    "pg-pool": "^2.0.3"

Test code

const request = require('supertest');
const app = require('server');

// close the server after each test
afterEach(async () => {
  await app.db.close();
});

const wFixture = [{
      "complexity": 3,
}];

describe('Controllers', () => {
  test('list get method', async () => {
    const response = await request(app).get('/');
    expect(response.status).toEqual(200);
    expect(response.body.count).toEqual(1);
    expect(response.body.data).toEqual(wFixture);
  });
});

[linkenneth]

I'm seeing the same issue here.

[SimenB]

We're not always able to point to user code - if it just shows dns it might be some polling or some such. Do you think you could put together a repo we could pull down showing the error?

[linkenneth]

Why is there DNS involved in filesystem polling anyways?

It's a bit difficult for me to isolate a repo for this, but it usually happens on functional tests with database setup in the beginning. My test itself looks like this:

import request from 'supertest';

import app from '../../app';
import knex from '../../knex';
import User from '../../models/user';

const userData = {/* ... */};

describe('/signup', () => {
  beforeEach(async () => {
    await knex.migrate.rollback();
    await knex.migrate.latest();
  });

  describe('GET', () => {
    test('should respond with 200 OK', async () => {
      await request(app).get('/signup').expect(200);
    });
  });

  describe('POST', () => {
    // TODO: create verifications and test these verifications
    test('should respond with 302 FOUND', async () => {
      await request(app).post('/signup').send(userData).expect(302);

      // TODO: test cookies set properly
    });

    test('should create the correct database entries', async () => {
      await request(app).post('/signup').send(userData);

      const users = await Promise.all([
        User.findByPrimaryEmail(userData.email),
        User.findByPrimaryPhone(userData.phone),
        User.findByPrimaryWeChat(userData.wechat),
        User.findByPrimaryQQ(userData.qq)
      ]);

      const userId = users[0].userId;
      expect(userId).toBeDefined();
      users.forEach((user) => expect(user.userId).toEqual(userId));
    });
  });
});

[NeoJRotary]

Same issue here. It is caused by mongodb in my case.
This simple code will make it.

const { MongoClient } = require('mongodb');
test('test', () => {});

module version
node : 10.4.0
mongodb : 3.0.10
jest : 23.1.0

[SimenB]

I'll also point out that this does not mean there's a bug in Jest - the flag exists to help you track down what's not cleaned up in your own code. I'm therefore closing this issue.

I have an open PR for fixing handles opened up within a test, which is currently not working: #6263

I'd still be interested in an example showing just DNSCHANNEL as it'd be great if we could improve it.

[vladyslav2]

In order to solve this issue, I found two critical problems in a project and one antipattern we've been using. Hope this information will help everyone who faced same issue:

• Instead of returning express().listener() we have been returning express() in server.js

Wrong version

const express = require('express');
const app = express();
app.listen(3000);
return app;

... in tests:
const server  = require('server');

Fixed version:

const express = require('express');
const app = express();
const server = app.listen(3000);
return server;

... in tests:
const server  = require('server');

• Antipattern where we have global database object

Wrong version:

global.db = await db.create();

Fixed version:

app.db = await db.create();

... inside tests
afterAll(() => {
  server._events.request.db.close();
});

[Sun1ive]

same issue here.
only happens when db models included in tests

test:

const { agent } = require('supertest');
const createApp = require('../../createApp');
// const models = require('../../models');

describe('Testing base routes', () => {
  const app = agent(createApp());

  test('successfully create app', async () => {
    const res = await app.get('/test');
    expect(res.status).toBe(200);
  });

  test('expect message to be OK', async () => {
    const res = await app.get('/test');
    expect(res.body.message).toBe('OK');
  });
});

result

yarn run v1.9.4
$ cross-env NODE_ENV=test jest tests/src --detectOpenHandles --forceExit
 PASS  tests/src/index.spec.js
  Testing base routes
    √ successfully create app (62ms)
    √ expect message to be OK (11ms)

Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        3.426s, estimated 4s
Ran all test suites matching /tests\\src/i.
Done in 4.89s.

include db models (sequelize + postgres)

const { agent } = require('supertest');
const createApp = require('../../createApp');
const models = require('../../models');

describe('Testing base routes', () => {
  const app = agent(createApp());

  test('successfully create app', async ()=> {
    const res = await app.get('/test');
    expect(res.status).toBe(200);
  });

  test('expect message to be OK', async () => {
    const res = await app.get('/test');
    expect(res.body.message).toBe('OK');
  });
});

result:

$ yarn test
yarn run v1.9.4
$ cross-env NODE_ENV=test jest tests/src --detectOpenHandles --forceExit
 PASS  tests/src/index.spec.js
  Testing base routes
    √ successfully create app (62ms)
    √ expect message to be OK (12ms)

Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        4.681s
Ran all test suites matching /tests\\src/i.

Jest has detected the following 1 open handle potentially keeping Jest from exiting:


  ●  DNSCHANNEL

      at dns.js:338:23

Done in 6.37s.

[SimenB]

If you put together a reproduction showing it, I can take a look at if it's possible to improve the message

[Raikhen]

Hey guys, does anyone know a solution for GraphQL Yoga? The server doesn't have a listen method, so we can't return it.

[johntran]

For Googlers:

I have a file db.ts that I mocked with db.js. db.ts opens up a database connection and causes this error to appear when db.ts is ran in a Jest test.

Renaming the mock file to db.ts fixed this issue for me.

[CatsMiaow]

test.spec.ts

// https://nodejs.org/docs/latest-v12.x/api/dns.html#dns_dns_promises_api
import { promises } from 'dns';

test('Node.js DNS', () => {
  const { Resolver } = promises;

  const resolver = new Resolver();
  expect(typeof resolver).toBe('object');

  const servers = resolver.getServers();
  console.log(servers);
});

I haven't found a way to close the open handle.
ava does not cause an error.

[szmarczak]

I think it's a bug in Jest since the process exits normally.

[sennett]

I was seeing this with node v12.10.0, using got and nock. Upgrading to node v14.9.0 resolved it for me.

[jean-smaug]

I was seeing this with node v12.10.0, using got and nock. Upgrading to node v14.9.0 resolved it for me.

Even when i upgrade to v14.9.0 I still got this problem.
I'm also using got in my project.

Did you change anything else ?

[sennett]

@jean-smaug This works for me:

  it('calls nock', async () => {
    nock(process.env.CRM_DOMAIN)
      .get('/crm/api/v1.0/clients')
      .reply(200, clientFixture)

    const response = await got(`${process.env.CRM_DOMAIN}/crm/api/v1.0/clients`)
    expect(JSON.parse(response.body)[0].firstName).toEqual('From nock')
  })

All the versions:

• nock@13.0.4
• got@11.5.2
• jest@26.4.2
• node v14.9.0 (installed via nvm)
• OSX 10.14.6

[mgcrea]

Can confirm that this issue still exists, in my case it does prevent jest to exit, thus requiring --forceExit:

Jest has detected the following 1 open handle potentially keeping Jest from exiting:

  ●  DNSCHANNEL

      at new CacheableLookup (node_modules/cacheable-lookup/source/index.js:75:14)
      at Object.<anonymous> (node_modules/got/dist/source/core/index.js:32:24)
      at Object.<anonymous> (node_modules/got/dist/source/as-promise/types.js:14:16)

with all up-to-date versions:

- nock@13.0.4
- got@11.8.0
- jest@26.6.3
- node v14.15.0 (node@14 via brew)
- OSX 10.15.7

[fungiboletus]

In my opinion, the issue is between jest and the DNS Resolver class in NodeJS the standard library.

got is not to blame there. It's simply a popular library using the Resolver class (which shouldn't be instantiated by default in got as it is not used by default but that's an issue for got).

@SimenB could it be possible to re-open this issue ?

const { Resolver } = require('dns').promises;

it('detects an open handle', () => {
  new Resolver();
  expect(true);
});

[SimenB]

@fungiboletus please open up a new issue - this has been closed for 2 years

[CatsMiaow]

It has been created as a new issue. #9982

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