# File lib/fakefs/pathname.rb, line 161
      def prepend_prefix(prefix, relpath)
        if relpath.empty?
          File.dirname(prefix)
        elsif /#{SEPARATOR_PAT}/o =~ prefix
          prefix = File.dirname(prefix)
          prefix = File.join(prefix, '') if File.basename(prefix + 'a') != 'a'
          prefix + relpath
        else
          prefix + relpath
        end
      end