Unit Test cases for websocket server "ws" library using jest

Question

I am trying to figure out how to write unit test cases for Websocket server which is using the ws library. I did go through jest-websocket-mock but I think this is for browser based APIs and I want to test server using JEST.

Basic Code: Server.js

import { createServer } from 'https';
import { WebSocketServer } from 'ws';
import { readFileSync } from 'fs';

const server = createServer({
  cert: readFileSync(config.certs.sslCertPath),
  key: readFileSync(config.certs.sslKeyPath),
});

const wss = new WebSocketServer({ noServer: true });

server.on('upgrade', (request, socket, head) => {
  const origin = request && request.headers && request.headers.origin;
  const corsRegex = <regex>;

  if (origin.match(corsRegex) != null) {
    wss.handleUpgrade(request, socket, head, (ws) => {
      wss.emit('connection', ws, request);
    });
  } else {
    socket.destroy();
  }
});

wss.on('connection', (ws, req) => {
  ws.on('message', (messageg) => {
    try {
      console.log(message);
    } catch (error) {
      console.log(error);
    }
  });

  ws.on('close', () => {
    console.log('close');
  });

  ws.on('error', (error) => {
    console.log(error);
  }); 
});

Can someone please help me with how can I test the original server?

How do you "test" a websocket from like the server? Don't you want to test the API's behaviors and responses on the client? — code, Oct 05 '22 at 03:51
I guess he wants to test is the if/else and that ws is called on message and close. But I would extract that and test it separately and trust WS and createServer — alextrastero, Oct 06 '22 at 09:43

Naor Tedgi · Answer 1 · 2022-10-07T18:23:35.077

you need to create some kind of dependency injection mechanism here lets for example move all the socket initialization logic into a separate function

function initSocketEvents(wss) {
    wss.on('connection', (ws, req) => {
        ws.on('message', (messageg) => {
            try {
                console.log(message);
            } catch (error) {
                console.log(error);
            }
        });

        ws.on('close', () => {
            console.log('close');
        });

        ws.on('error', (error) => {
            console.log(error);
        });
    });
    return wss;
}

now at the server initilization just call the function from a different file

...

const {initSocketEvents}  = require("./socket-handler") 
const wss = new WebSocketServer({ noServer: true });
initSocketEvents(was);

...

everything stays the same except the fact its way much easier to test it now at the test file

const {initSocketEvents}  = require("./socket-handler") 
const { assert } = require('console');
const { EventEmitter } = require('events');
class MyTestWebSocket extends EventEmitter { }
const mockWSS = new MyTestWebSocket()
initSocketEvents(mockWSS)
mockWSS.emit('connection', mockWSS)
assert(mockWSS.listenerCount('connection')===1)
assert(mockWSS.listenerCount('message')===1)
assert(mockWSS.listenerCount('close')===1)
assert(mockWSS.listenerCount('error')===1)

now it should be straightforward to separate each listener's logic and inject it outside the function and then assert the desired logic.

Unit Test cases for websocket server "ws" library using jest

1 Answers1