websockets stress (load) test (node.js)

I have an node.js application based on websockets. I need to do load test for this application. There are three basic points which need to be tested: 1. websocket clients connect to server and server sends back success/error connection message with a little help data (json). 2. Every 1/2 seconds each connected client pings server and server sends response to client. 3. There is also a manager client who broadcasts messages to all connected clients. For these points I need to check latency of messages send/receive. For third point also need to check delay between each client message receive.

I am using http://ift.tt/1AM8BIF node.js module , websocket server implemented on node.js native cluster module. Broadcasting done by simple foreach through connected clients in each forked worker. Also I need to know apx. how many clients can handle my server. So I want to understand is there any test modules/tools that can help me to achieve my goal . Thanks.