ActiveRecord::Enum matcher

Hi guys,

I started a matcher for the  [ActiveRecord::Enum](http://edgeapi.rubyonrails.org/classes/ActiveRecord/Enum.html). I know we can`t merge this now since no released rails 4.1.0.

I only want to show you guys the idea =) and ask one thing: ActiveRecord::Enum is only on rails 4.1.0, how we can skip this specs in older rails versions?
I guess this is not possible. Before the call to `define_model` I have access to the `enum_attribute` inside the `define_model` I receive `NameError: undefined local variable or method `enum_attribute' for RecordWithArrayValue(id: integer):Class`.