Change the implementation of a classes instance method by including a module.

simplify_me.rb

# original ApplicationController
class ApplicationController
  def home_page?
    "original"
  end
end

puts ApplicationController.new.home_page?
# => original

# define a new implementation of home_page? outside of ApplicationController.
# the goal is to be able to test it independently, by including it into a very simple class.
module I18nModule
  def self.included(base)
    base.class_eval do
      def home_page?
        "i18ned"
      end
    end
  end
  # i'd prefer to do this, but that way the method ends up _behind_ the original home_page? in the method lookup list.
  # so this only works for methods that don't already exist on the class.
  #def home_page?
  #  "i18ned"
  #end
end

class ApplicationController
  include I18nModule
end

puts ApplicationController.new.home_page?
# => i18ned