Jest detects open handle with Express app

Question

I've been trying to figure this out for a while now, but with no luck. I initially had the issue when performing simple integration tests with a MongoDB database, but I've stripped the code right down and made it as simple as I can. The only thing I have running is a single test file:

// blah.test.js
const express = require('express');
const app = express();

describe('test block', () => {
    let server = null;

    beforeEach(() => {
        server = app.listen(3000, () => console.log('Listening on port 3000'));
    });

    afterEach(async () => {
        await server.close();
    });

    it('should pass the test', () => {
        expect(1).toBe(1);
    });
});

The test passes, but Jest informs me of an open handle which could prevent it from exiting:

On this occasion, it did exit, but still notices an open handle. I would like to know how to safely close this, without forcing exit. With previous tests, I would get the same open handle warning, but also with an error stating that Jest didn't exit one second after completing the tests.

I also tried using beforeAll() and afterAll(), instead of beforeEach() and afterEach(), but still get the same problem. I know the test doesn't require the server on this occasion, but I was trying to make it as simple as possible to try to find the issue with opening and closing the server.

UPDATE: I noticed that it seems to work fine as soon as I add a second test file:

// blah2.test.js
const express = require('express');
const app = express();

describe('test block', () => {
    let server = null;

    beforeEach(() => {
        server = app.listen(3000, () => console.log('Listening on port 3000'));
    });

    afterEach(async () => {
        await server.close();
    });

    it('should pass the test', () => {
        expect(2).toBe(2);
    });
});

No open handles with two tests running

If anyone can share any ideas as to why this happens, it would be much appreciated.

I am using:

Express: 4.16.3

Jest: 23.5.0

NPM: 6.3.0

Answer 1

So I solved the issue by abstracting all the app logic to an app.js file:

const express = require('express');
const routes = require('./routes');
const app = express();

app.use('/api', routes);

module.exports = app

Then creating a server.js file with all my server logic:

const app = require('./app.js')
const PORT = process.env.PORT || 3000
app.listen(PORT, () => console.log(`Listening on port: ${PORT}`))

Then just import app.js into your test file like this:

const app = require('../app.js')

Works like a charm!