Using Cypress with `mock-sockets` - websocket

Question

I am trying to use mock-sockets with Cypress, setting up the mock in the onBeforeLoad hook for cy.visit() in my beforeEach block. I can get one test to work but when the mock setup runs on the next beforeEach I get an error that A mock server is already listening on this url.
code under test:
(called from my React app's componentDidiMount)
subscribeToSettings(url: string): W3CWebSocket {
let settingsSubscription = new W3CWebSocket(url);
settingsSubscription.onopen = () => console.log('WebSocket Client Connected (settings)');
settingsSubscription.onclose = () => console.log('WebSocket Client Disconnected (settings)');
settingsSubscription.onmessage = (message: MessageEvent) => this.handleSettingsMessage(message);
return settingsSubscription;
}
/**
* Handler for websocket settings messages, which updates the local settings values.
* #param message the websocket message
*/
handleSettingsMessage(message: MessageEvent) {
const updatedValues = JSON.parse(message.data);
console.log('A message was received on the settings channel.', updatedValues);
this.props.updateSettingsFromBackend(updatedValues);
}
cypress tests
import { Server } from 'mock-socket'
import { defaultSettingsState } from "../../src/reducers/settings.reducer";
import { _createSettingsApiPutPayload } from "../../src/actions/settings.actions";
describe('mock socket method 1', () => {
let mockSocket;
let mockServer;
beforeEach(() => {
cy.visit('/', {
onBeforeLoad(win: Window): void {
// #ts-ignore
cy.stub(win, 'WebSocket', url => {
mockServer = new Server(url)
mockServer.on('connection', socket => {
console.log('mock socket connected');
mockSocket = socket;
});
mockSocket = new WebSocket(url);
return mockSocket
});
},
});
});
afterEach(() => {
mockSocket.close()
mockServer.stop()
});
it('gets a message', () => {
cy.contains('SETTINGS').click()
const object = _createSettingsApiPutPayload(defaultSettingsState)
mockSocket.send(JSON.stringify(object));
cy.contains('Motion threshold')
});
it('gets another message', () => {
cy.contains('SETTINGS').click()
const object = _createSettingsApiPutPayload(defaultSettingsState)
mockSocket.send(JSON.stringify(object));
cy.contains('Motion threshold')
});
});
Here are the logs from my console:
WebSocket Client Connected (settings)
mock socket connected at url ws://localhost:8702/PM_Settings
A message was received on the settings channel. {…}
mock socket connected at url ws://localhost:3000/sockjs-node/949/mhuyekl3/websocket
The development server has disconnected.
Refresh the page if necessary.
Uncaught Error: A mock server is already listening on this url
I wonder if it has to do with that second call which is for some mystery url.
(Note: calling cy.contains('SETTINGS').click() at the end of beforeEach somehow doesn't work, even in that first test. Even when I have my app set to start on the settings page (instead of having to click to it from inside the tests), clicking on SETTINGS from beforeEach still doesn't work even though we're already there. So that's kind of weird)
These cypress logs may also be helpful:

Answer 1

It only worked for me, when I moved server stopping into WebSocket stub:
cy.stub(window, 'WebSocket', url => {
if (mockServer) {
mockServer.stop();
}
mockServer = new Server(url);
mockServer.on('connection', socket => {
mockSocket = socket;
});
mockSocket = new WebSocket(url);
return mockSocket;
});
Im probably wrong, but I guess afterEach or mockServer.stop(); is async thats why mock server fails to stop before new init