We have express app:

import _ from ‘lodash‘
import faker from ‘faker‘
import express from ‘express‘
import bodyParser from ‘body-parser‘
import getTokenFromHeader from ‘../../src/routes/utils/get-token-from-header‘

export default startServer

const users = _.times(20, () => faker.helpers.contextualCard())
const userAuth 
 
= {
  username: ‘jane‘,
  password: ‘I have a secure password‘,
}
const user = {
  token: ‘Wanna-hear-a-secret?-I-sometimes-sing-in-the-shower!‘,
}

function startServer() {
  const app = express()

  app.use(bodyParser.json())

  function auth(req, res, next) {
    const token = getTokenFromHeader(req)
    
 
if (!token || token !== user.token) {
      res.sendStatus(401)
    } else {
      next()
    }
  }

  const userRouter = express.Router()
  userRouter.get(‘/‘, (req, res) => {
    const {query: {limit = 20, offset = 0}} = req
    res.json({users: _.take(users.slice(offset), limit)})
  })

  
 
// Preload user objects on routes with ‘:username‘
  userRouter.param(‘username‘, (req, res, next, param) => {
    req.user = users.find(({username}) => username === param)
    next()
  })

  userRouter.get(‘/:username‘, (req, res) => {
    if (req.user) {
      res.json({user: req.user})
    } else {
      res.sendStatus(404)
    }
  })

  userRouter.post(‘/‘, auth, (req, res) => {
    users.unshift(req.body.user)
    res.json({user: users[0]})
  })

  userRouter.delete(‘/:username‘, auth, (req, res) => {
    users.splice(users.indexOf(req.user), 1)
    res.json({success: true})
  })

  const authRouter = express.Router()
  authRouter.post(‘/‘, (req, res) => {
    if (
      req.body.username === userAuth.username &&
      req.body.password === userAuth.password
    ) {
      res.json({user})
    } else {
      res.sendStatus(401)
    }
  })

  const apiRouter = express.Router()
  apiRouter.use(‘/users‘, userRouter)
  apiRouter.use(‘/auth‘, authRouter)

  app.use(‘/api‘, apiRouter)

  return new Promise(resolve => {
    const server = app.listen(3001, () => {
      resolve(server)
    })
  })
}

As you can see, we wrap Express App into a function ‘startServer‘ and export it as default export. The return value of this function is the server which wrap into a Promise.

The good part for doing this way is that we can start and stop server whenever we want to prevent menory leak or "ADDRESS IN USED" problem.

import startServer from ‘../start-server‘
import axios from ‘axios‘

let server

beforeAll(async () => {
    server = await startServer()
})

afterAll(done => server.close(done))

test(‘can get users‘, async () => {
    const user = await axios
        .get(‘http://localhost:3001/api/users‘)
        .then(response => response.data.users[0])

    // toMatchObject, to check whether user object
    // has ‘name‘ prop which is a string
    // and ‘username‘ prop which is a string
    // this is a subset, doesn‘t need to match all the object props
    expect(user).toMatchObject({
        name: expect.any(String),
        username: expect.any(String)
    })
})

// Test offset and limit should work
// first get 5 users
// then get last two users by given limit and offset
// then check tow users and equal to last tow user in five users.
test(‘get users, limit and offset should work‘, async () => {
    const fiveUsersPromise = axios
        .get(‘http://localhost:3001/api/users?limit=5‘)
        .then(response => response.data.users)
    const twoUsersPromise = axios
        .get(‘http://localhost:3001/api/users?limit=2&offset=3‘)
        .then(response => response.data.users)

    const response = await Promise
        .all([fiveUsersPromise, twoUsersPromise])
    const [fiveUsers, twoUsers] = response
    const [, , ,firstFiveUser, secondFiveUser] = fiveUsers
    const [firstTwoUser, secondTwoUser] = twoUsers
    expect(firstTwoUser).toEqual(firstFiveUser)
    expect(secondFiveUser).toEqual(secondTwoUser)
})

In the test, we call ‘beforeAll‘ to start the server and ‘afterAll‘ to close the server.

[Node & Testing] Intergration Testing with Node Express