Unit Test cases for websocket server "ws" library using jest - node.js

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?

Answer 1

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.