helper.rb

def fixture_file_upload_fg(name, options = {})
  path = File.join(File.dirname(__FILE__), 'fixtures', 'files', name)
  m = Module.new do
    define_method :content_type do
      options[:content_type] || 'application/x-shockwave-flash'
    end

    define_method :original_filename do
      name
    end

    define_method :size do
      File.size(path)
    end
  end

  File.open(path).extend(m)
end