fabricator.rb

Fabricator(:product) do 
  items(:count => 1) { Fabricate(:item) }
end

Fabricator(:item) do 
  name "An Item"
end

models.rb

class Product < ActiveRecord::Base
  has_many :items

  def self.has_items
    self.items.available.count
  end
end

class Item < ActiveRecord::Base
  belongs_to :product

  scope :available, where(:available => true)
end

If your test ever calls Product#has_items it will error on L5 (of models.rb) saying that you cannot call .available on

Try changing has_items to an instance method and see if that fixes the problem.