mock_uploader.rb

  def mock_uploader(file, type = 'image/png')
    filename = "%s/%s" % [ File.dirname(__FILE__), file ]
    uploader = ActionController::UploadedStringIO.new
    uploader.original_path = filename
    uploader.content_type = type
    def uploader.read
      File.read(original_path)
    end
    def uploader.size
      File.stat(original_path).size
    end
    uploader
  end