# File lib/paperclip/matchers/validate_attachment_content_type_matcher.rb, line 41
        def failure_message
          "".tap do |str|
            str << "Content types #{@allowed_types.join(", ")} should be accepted" if @allowed_types.present?
            str << "\n" if @allowed_types.present? && @rejected_types.present?
            str << "Content types #{@rejected_types.join(", ")} should be rejected by #{@attachment_name}" if @rejected_types.present?
          end
        end