# File lib/paperclip/matchers/validate_attachment_presence_matcher.rb, line 45
        def no_error_when_valid?
          @file = StringIO.new(".")
          @subject.send(@attachment_name).assign(@file)
          @subject.valid?
          @subject.errors["#{@attachment_name}_file_name""#{@attachment_name}_file_name"].blank?
        end