During the recent airhacks workshops an attendee asked me a question about websocket stress testing tools.
You could create an own generator with jmeter.apache.org, but the websocket protocol is not directly supported.
The first, experimental, version of hellsockets is available. It is based on the built-in Java EE 7 websocket client and porcupine.
Hellsocket is a 23kB WAR which can be installed as drop-in on a Java EE 7 server and was tested on GlassFish / Payara 4.1 and WildFly 8.2. Stress tests can be initiated and the statistics are available via: HTTP/REST.