https://gist.github.com/hiredman/60e5e6f0025cb38c8a7739d21f5a8ce6 is a little thing I've been toying with for using spec to define and check stateful protocols, meaning it defines how a client and server communicate, and certain client requests are only valid when the server is in certain states. given such a definition you stick it between your client and server and it checks the communication back and forth and gives errors if either side violates the protocol.