Have you checked your rapidsms.log file? When you send the HELP message through the message tester app web interface, do you see HelpHandler being registered? Do you see the handle phase of the message processing start? Do you see the handlers app running during the handle phase?
rapidsms.router.blocking.router INFO Incoming (426838 via message_tester): HELP
......
rapidsms.router.blocking.router DEBUG In handle phase
rapidsms.router.blocking.router DEBUG In <app: tut> app
rapidsms.router.blocking.router DEBUG In <app: handlers> app
rapidsms.router.blocking.router DEBUG Short-circuited
rapidsms.router.blocking.router DEBUG In default phase
rapidsms.router.blocking.router DEBUG Skipping phase
......
Based on that, can you tell what part of the process is not working? I hope that helps
Alex Lemann