7.1.1 • Public • Published

Javascript mocking library for websockets and


This is basically mock-socket made to work with apollo subscriptions-transport-ws. The implementation is not perfect, which was noticed over two years ago by @brian-mann of : . Since two years later this architectural problem is still not fixed, I've decided to fork with the tiny change that's just enough to make it work in this specific usecase. Thanks @thoov for the amazing work on this package! I actually started writing my own websocket server implementation, when, after a half day of happy hacking I came to realization "this is nodejs.. someone had to got this to work before me", and there it was. :)


npm install mock-socket-with-protocol --dev


To use within a node environment you can simply import or require the files directly. This option is great for phantomjs or CI environments.

import { WebSocket, Server, SocketIO } from 'mock-socket-with-protocol';
// OR
const mockServer = require('mock-socket-with-protocol').Server;
const socketIO = require('mock-socket-with-protocol').SocketIO;
const mockWebSocket = require('mock-socket-with-protocol').WebSocket;

Native WebSocket Example

// chat.js
function Chat() {
  const chatSocket = new WebSocket('ws://localhost:8080');
  this.messages = [];
  chatSocket.onmessage = (event) => {
// chat-test.js
import { Server } from 'mock-socket-with-protocol';
describe('Chat Unit Test', () => {
  it('basic test', (done) => {
    const mockServer = new Server('ws://localhost:8080');
    mockServer.on('connection', server => {
      mockServer.send('test message 1');
      mockServer.send('test message 2');
    // Now when Chat tries to do new WebSocket() it
    // will create a MockWebSocket object \
    var chatApp = new Chat();
    setTimeout(() => {
      const messageLen = chatApp.messages.length;
      assert.equal(messageLen, 2, '2 messages where sent from the s server');
    }, 100);

Socket.IO Example

// chat.js
function Chat() {
  const chatSocket = new io('http://localhost:8080');
  this.messages = [];
  chatSocket.on('chat-message', data => {
// chat-test.js
import { SocketIO, Server } from 'mock-socket-with-protocol';
describe('Chat Unit Test', () => {
  it('basic test', (done) => {
    const mockServer = new Server('http://localhost:8080');
    mockServer.on('connection', server => {
      mockServer.emit('chat-message', 'test message 1');
      mockServer.emit('chat-message', 'test message 2');
      This step is very important! It tells our chat app to use the mocked
      websocket object instead of the native one. The great thing
      about this is that our actual code did not need to change and
      thus is agnostic to how we test it.
    */ = SocketIO;
    // Now when Chat tries to do io() or io.connect()
    // it will use MockSocketIO object
    var chatApp = new Chat();
    setTimeout(() => {
      const messageLen = chatApp.messages.length;
      assert.equal(messageLen, 2, '2 messages where sent from the server');
    }, 100);

Working with the source code

Local builds

The easiest way to work on the project is to clone the repo down via:

git clone
cd mock-socket-with-protocol

Then to create a local build via:

yarn build

Then create a local npm link via:

yarn link

At this point you can create other projects / apps locally and reference this local build via:

yarn link mock-socket-with-protocol

from within your other projects folder. Make sure that after any changes you run yarn build!


This project uses mocha as its test framework. Tests are located in /test and have 1 of 3 file name prefixes (functional-, issue-#, or unit-).

yarn test


This project uses eslint and a rules set from airbnb's javascript style guides. To run linting:

yarn lint


This project uses prettier with --single-quote and --print-width 120. To run the formatting:

yarn format

Code Coverage

Code coverage reports are created in /coverage after all of the tests have successfully passed. To run the coverage:

yarn test:coverage

Feedback / Issues

If you have any feedback, encounter any bugs, or just have a question, please feel free to create a github issue

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  • lgandecki