[RSpec][FactoryGirl] クラスは異なるが名前が等しい属性をそれぞれsequenceする ref: http://qiita.com/kidachi_/items/212e5ffa7d2cd4937726

configuration.rb

module FactoryGirl
  # @api private
  class Configuration
    attr_reader :factories, :sequences, :traits, :strategies, :callback_names

    def initialize
      @factories      = Decorator::DisallowsDuplicatesRegistry.new(Registry.new('Factory'))
      @sequences      = Decorator::DisallowsDuplicatesRegistry.new(Registry.new('Sequence'))
      @traits         = Decorator::DisallowsDuplicatesRegistry.new(Registry.new('Trait'))
      @strategies     = Registry.new('Strategy')
      @callback_names = Set.new
      @definition     = Definition.new

      to_create { |instance| instance.save! }
      initialize_with { new }
    end
  ~
end

default.rb

        def sequence(name, *args, &block)
          FactoryGirl.register_sequence(Sequence.new(name, *args, &block))
        end

disallows_duplicates_registry.rb

module FactoryGirl
  class Decorator
    class DisallowsDuplicatesRegistry < Decorator
      def register(name, item)
        if registered?(name)
          raise DuplicateDefinitionError, "#{@component.name} already registered: #{name}"
        else
          @component.register(name, item)
        end
      end
    end
  end
end

factories.rb

  sequence(:categories) { |n| "test_category_#{n}" }
  factory :category do
    name {generate(:categories)}
    ~
  end

  sequence(:tags) { |n| "test_tag_#{n}" }
  factory :tag do
    name {generate(:tags)}
    ~
  end

file1.txt

 $ spring rspec spec/hoge_spec.rb
/Users/kidachi_/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/factory_girl-4.4.0/lib/factory_girl/decorator.rb:10:in `method_missing': Sequence already registered: name (FactoryGirl::DuplicateDefinitionError)

file2.txt

 $ spring rspec spec/hoge_spec.rb
/Users/kidachi_/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/factory_girl-4.4.0/lib/factory_girl/decorator.rb:10:in `method_missing': Sequence already registered: name (FactoryGirl::DuplicateDefinitionError)

methods.rb

      # Generates and returns the next value in a sequence.
      #
      # Arguments:
      #   name: (Symbol)
      #     The name of the sequence that a value should be generated for.
      #
      # Returns:
      #   The next value in the sequence. (Object)
      def generate(name)
        FactoryGirl.sequence_by_name(name).next
      end