duleja: Sessions are not authoritative. Just having a number in a session doesn't mean the user with a corresponding ID exists. You'll need to hit your DB to grab the user information just to be sure that is actually a user, that hasn't been deleted, that the user has not been blocked, etc...
There's the crux of what people have been advising you. If you're not sure what the situations are, I'd recommend working within guidelines that have been shown to work for most apps. :-)
I'm sure this is some kind of pre-caffeine fog, but I'm having an issue with `require`. If I `puts File.expand_path('../../../02_karate_chop/karate_chop.rb', __FILE__)` I'll get /Users/username/Dev/code_kata/ruby/02_karate_chop/karate_chop.rb
If I use require instead of puts I get a LoadError but the file path is different: /Users/username/Dev/code_kata/02_karate_chop/karate_chop.rb (note the absence of /ruby/)
I wasn't looking closely enough at the stack trace. Got so caught up on the error being the same that I didn't notice that one error was coming from one file and one from a different file with a nearly identical name.