categories_controller.rb

class CategoriesController < ApplicationController

  before_filter :find_category, :only => [:show]
  before_filter :ensure_current_post_url, :only => :show

  def show
    @products = @category.products.paginate :page => params[:page], :order => Product.pagination_ordering(session[:prefs][:product_sort]) if @category
  end

  private
    def find_category
      @category = Category.find(params[:id]) if params[:id]
    end
    
    def ensure_current_post_url

      redirect_to @category, :status => :moved_permanently unless @category.friendly_id_status.best?
    end
end

category.rb

class Category < ActiveRecord::Base

  acts_as_tree :order => "name"

  has_many :category_products
  has_many :products, :through => :category_products

  has_friendly_id :name, :use_slug => true

  validates_presence_of :name
  validates_uniqueness_of :name, :scope => :parent_id

  validate :parent_category_is_not_self
  

  def root?
    parent.nil?
  end
  
  private
  
    def parent_category_is_not_self
      errors.add(:parent_id, "Category can not be it's own parent") if parent_id == id and not id.nil?
    end

end

cucumber output

Given there is a category                                   # features/step_definitions/general.rb:48
And it has name set to "Tapes & Adhesives"                  # features/step_definitions/general.rb:62
When I view the url "/categories/tapes-adhesives.html"      # features/step_definitions/general.rb:92
Then I should see the category page for "Tapes & Adhesives" # features/step_definitions/seo.steps.rb:1
Given there is a category                                   # features/step_definitions/general.rb:48
And it has name set to "Tapes Adhesives"                    # features/step_definitions/general.rb:62
When I view the url "/categories/tapes-adhesives--2.html"   # features/step_definitions/general.rb:92
  10 redirects to the same URL ("http://www.example.com/categories/tapes-adhesives--2.html") (Webrat::InfiniteRedirectError)
  (eval):2:in `visit'
  ./features/step_definitions/general.rb:93:in `/^I view the url "([^\"]*)"$/'
  features/seo/url.feature:35:in `When I view the url "/categories/tapes-adhesives--2.html"'