Functional Testing is a very powerful tool in general. It allows performing validation tests for HTTP responses, locating of broken connections and even generating of a number of concurrent requests. And if testing of the stateless HTTP request/response protocol is not a rocket science, testing of WebSockets could be problematic, because messages need to be tested on both sides: client and server. In my talk, I would like to share an experience of how we do it in my current team using Contract Testing pattern and Erlang OTP. Life demo is included, of course.