test_helper.rb

class ActiveSupport::TestCase
  def setup
    clear_all_collections
  end
  
  def clear_all_collections
    # ruby 1.9 compatability
    Dir[File.join(Rails.root, 'app/models/**/*.rb')].each do |model_path|
      klass = File.basename(model_path, '.rb').classify.constantize
      klass.collection.remove if klass.respond_to?(:collection)
    end
  end
end