How do I test authentication failures in Socket.io?
Connect a Socket.io client with an invalid token in the auth option. Listen for the 'connect_error' event. Assert that the error message is 'Authentication failed' or similar. Disconnect the bad socket after the test.
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More FAQs in Testing and Debugging the Chat Feature Socket.io and Real-Time Messaging
Create test users with JWT tokens, connect Socket.io clients with io() and auth, emit events (join:chat, message:send) and assert received events (message:received) using done callbacks. Test typing indicators, authentication failures, and message persistence. Clean up sockets and server in afterAll.
Check that both sockets joined the same room (log room members with io.sockets.adapter.rooms.get(roomId)). Verify the room ID is the same for both users (check getRoomId function). Ensure the socket didn't disconnect. Check CORS configuration. Verify the event name matches exactly.
You're not cleaning up Socket.io listeners. In React useEffect, return a cleanup function that calls socket.off('message:received', handler) with the specific handler reference. Without cleanup, listeners accumulate on re-renders, causing messages to appear multiple times.
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