Update test_msg.
Update test_msg.

* Add missing require so that it passes again.
* Change namespaced key lookups to be more explicit.

mysociety/ruby-msg,zhivko/ruby-msg,aquasync/ruby-msg,packages/ruby-msg,TheProjecter/ruby-msg,aquasync/ruby-msg,zhivko/ruby-msg,mvz/ruby-msg,TheProjecter/ruby-msg,mysociety/ruby-msg,mvz/ruby-msg,packages/ruby-msg