How do I fix: "TypeError: wsModule.Server is not a constructor" when running tests in Jest

I'm new to Jest and I want to start writing some integration tests for a Node.js server. When I try and run a test, I receive a "TypeError: wsModule.Server is not a constructor" error. Why won't my test environment initialise the socket server?

server.js:

const app = require('express')();
const server = require('http').Server(app);
const io = require('socket.io')(server);
const router = require('./router/router');
const bodyParser = require('body-parser');
const cors = require('cors');
require('./socket/socket')(io); <-- TEST FAILS BECAUSE OF SOCKET MODULE

// Allow CORS so our client can consume JSON
app.use(cors())

// Takes the raw requests and turns them into usable properties on req.body
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));

// Use our router
app.use('/', router);

server.listen(3000, (req, res) => {
  console.log("listen at 3000!");
});

module.exports = app;

socket.js:

const userService = require('../services/userService');
const roomService = require('../services/roomService');

module.exports = function (io) {

  io.on("connection", socket => {

    console.log('there has been a connection with: ' + socket.id);

    socket.on('set-username', ({ roomId, username }) => {
      userService.setUsername(roomId, username, socket, io);
    });

    socket.on('start-game', ({ roomId, hostName }) => {
      roomService.startGame(roomId, hostName, socket, io);
    });

});

roomService.test.js:

const chai = require('chai');
const chaiHttp = require('chai-http');
const server = require('../../server');
const { expect } = chai;
chai.use(chaiHttp);

describe("example", () => {
  test('should run', () => {
    expect(true).to.be.true;
  })
})