Server instances, jest and 'listen EADDRINUSE :::3000'

Question

Am new to jest, node and express, and am having a problem with testing my app.

The actual code seems to be working - it's just when passing the server instance to each of the test files (user.test.js and genres.test.js) and running jest, the port is being blocked. I assume it's because I'm creating duplicate instances of the server in each test file, without realising it.

Running jest with the flag --runInBand works, and so does only using one test file, but this doesn't help me understand exactly what's going on.

I've posted example code below, but I'm struggling to cut it down, however I do think most of the code is irrelevant, and it's just down to how I'm passing the server to each file.

Again, apologies for the length, but I think it should be very basic for anyone but me! Thanks.

---

index.js (.)

const express = require('express');
const app = express();
const genres = require('./routes/genres');
const users = require('./routes/users');
app.use(express.json());
app.use('/api/genres', genres);
app.use('/api/users', users);

const port = process.env.PORT || 3000;

const server = app.listen(port, () => console.log(`Listening on port ${port}...`));
console.log(typeof server);
// export server to be used in test file
module.exports = server;

genres.js (./routes)

const express = require('express');
const router = express.Router();

router.post('/', async (req, res) => {
    res.send('post genre ok');
});

module.exports = router;

users.js (./routes)

const express = require('express');
const router = express.Router();

router.post('/', async (req, res) => {
    res.send('post user ok');
});

module.exports = router;

genres.test.js (./tests)

const request = require('supertest');

let server;

describe('auth tests', () => {

    const exec = async function(){
        return await request(server)
            .post('/api/genres');
    };

    beforeEach(() => {
        server = require('../index');
    });
    afterEach(async () => {
        await server.close();
    });

    describe('POST /', () => {
        it('should return 200', async () => {
            const res = await request(server).post('/api/genres');
            expect(res.status).toBe(200);
        });
    });
});

user.test.js (./tests)

const request = require('supertest');

let server;

describe('user tests', () => {

    const exec = async function(){
        return await request(server)
            .post('/api/user');
    };

    beforeEach(() => {
        server = require('../index');
    });
    afterEach(async () => {
        await server.close();
    });

    describe('POST /', () => {
        it('should return 200', async () => {
            const res = await request(server).post('/api/users');
            expect(res.status).toBe(200);
        });
    });
});

Answer 1

希望这一点（第2点）可以帮助其他人解决这个问题

通过从服务器拆分应用程序，它对我有用。我不确定这是否是正确的方法，也不确定100％为什么适用于应用程序而不是服务器，但是我的所有测试现在都通过了。

index.js现在是app.js：

const express = require('express');
const app = express();
const genres = require('./routes/genres');
const users = require('./routes/users');
app.use(express.json());
app.use('/api/genres', genres);
app.use('/api/users', users);

// export server to be used in test file
module.exports = app;

服务器被分为另一个文件：

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

const port = process.env.PORT || 3000;

app.listen(port, () => console.log(`Listening on port ${port}...`));

然后测试文件将导入应用程序而不是服务器。因此，每个测试都不会创建自己的实例。

NB：我认为 -我真的不知道这有多正确，但是如上所述