race_condition_collection.rb

# Simulates a race condition for testing.  The first try always fails, the second try succeeds.
#
# Abstract example:
#
#     RaceConditionCollection.new(active_record_model.associated_collection)
#
# Concrete example:
#
#     RaceConditionCollection.new(blog_post.comments)
class RaceConditionCollection
  def initialize(collection)
    @collection = collection
    @tried = false
  end

  def method_missing(method, args)
    if @tried
      @collection.send(method, args)
    else
      @tried = true
      raise ActiveRecord::RecordNotUnique
    end
  end
end