Problem Testing Active Merchant using peepcode pdf example

I am trying to set up ActiveMerhcant in my RoR application and using
the tests that come with the peepcode PDF. I am getting an error when
I run rake test that I don't know what to do with, and I am hoping
someone can give me some guidance.

The application also uses acts_as_state_machine - and I think the
problem lies there

uninitialized constant Rails::Initializer::ScottBarron
dependencies.rb:477:in `const_missing'
acts_as_state_machine/trunk/init.rb:4:in `load_plugin'
acts_as_state_machine/trunk/init.rb:3:in `class_eval'
acts_as_state_machine/trunk/init.rb:3:in `load_plugin'

I googled for Scott Barron, and I can see he has been a significant
contributor , but I don't know how to interpret or resolve this.