# File lib/logging/appenders/file.rb, line 25
    def self.assert_valid_logfile( fn )
      if ::File.exist?(fn)
        if not ::File.file?(fn)
          raise ArgumentError, "#{fn} is not a regular file"
        elsif not ::File.writable?(fn)
          raise ArgumentError, "#{fn} is not writeable"
        end
      elsif not ::File.writable?(::File.dirname(fn))
        raise ArgumentError, "#{::File.dirname(fn)} is not writable"
      end
      true
    end