Test page helpers in rails app

Question

I have some page helpers in application, something such as:

# ajax_helper.rb
module AjaxHelper
  def update_counter(new_value)
    page.replace_html :counter, :partial => 'counter', :locals => { :value => new_value}
  end
end

# update.fbjs.rjs
....
page.update_counter(new_value)
.....

What is the best way to test this helper method?