WebSocket & gRPC Testing

Generate a JMeter test plan for WebSocket load testing:

WebSocket URL: [ws://localhost:8080/ws or wss://]
Flow:
1. Connect to WebSocket
2. Send message: [payload]
3. Wait for response containing [substring]
4. Send [N] more messages
5. Close connection

Requirements:
- Use JMeter WebSocket Sampler plugin (Peter Doornbosch)
- Connection and close samplers
- Response assertion on incoming message
- Simulate [N] concurrent connections
- Think time between messages: [N]ms
- Extract dynamic values from connect response