How to fix err Jest has detected the following 3 open handles potentially keeping Jest from exiting

Question

Just starting to work on some node app using jest for testing. express-generator used for scaffolding.
On first test I get following error:

Jest has detected the following 3 open handles potentially keeping Jest from exiting

Steps to reproduce:

git clone [email protected]:gandra/node-jest-err-demo.git   
cd node-jest-err-demo       
npm install   
cp .env.example .env    
npm run test  

npx envinfo --preset jest output:

npx: installed 1 in 1.896s

  System:
    OS: macOS High Sierra 10.13.4
    CPU: x64 Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz   Binaries:
    Node: 9.3.0 - /usr/local/bin/node
    Yarn: 1.5.1 - /usr/local/bin/yarn
    npm: 5.7.1 - /usr/local/bin/npm   npmPackages:
    jest: ^23.1.0 => 23.1.0

Any idea how to fix it?

Here is related issue on github: https://github.com/facebook/jest/issues/6446

Answer 1

detectOpenHandles option is used to detect open handles, it should be normally used. The error warns about potentially open handles:

Jest has detected the following 4 open handles potentially keeping Jest from exiting

Even if the handles will be closed, the error will still appear.

The actual problem with this application is that database connection isn't really closed:

if (process.env.NODE_ENV === 'test') {
  mongoose.connection.close(function () {
    console.log('Mongoose connection disconnected');
  });
}

For some reason NODE_ENV is dev, despite that the documentation states that it's expected to be test.

Closing database connection immediately on application start may cause problems in units that actually use database connection. As explained in the guide, MongoDB connection should be at the end of test. Since default Mongoose connection is used, it can be:

afterAll(() => mongoose.disconnect());