added user_is_following method, added 2 model specs

app/controllers/tags_controller.rb

@@ -40,10 +40,7 @@ class TagsController < ApplicationController
   end
 
  def tag_followed?
-   if @tag_followed.nil?
-     @tag_followed = TagFollowing.joins(:tag).where(:tags => {:name => params[:name].downcase}, :user_id => current_user.id).exists?
-   end
-   @tag_followed
+   TagFollowing.user_is_following?(current_user, params[:name])
  end
 
   def prep_tags_for_javascript

app/models/tag_following.rb

@@ -3,4 +3,9 @@ class TagFollowing < ActiveRecord::Base
   belongs_to :tag, :class_name => "ActsAsTaggableOn::Tag"
 
   validates_uniqueness_of :tag_id, :scope => :user_id
+  
+  def self.user_is_following?(user, tagname)
+    tagname.nil? ? false : joins(:tag).where(:tags => {:name => tagname.downcase}, :user_id => user.id).exists?
+  end
+  
 end

spec/models/tag_following_spec.rb

@@ -13,4 +13,13 @@ describe TagFollowing do
   it 'allows multiple tag followings for different users' do
     TagFollowing.new(:tag => @tag, :user => bob).valid?.should be_true
   end
+
+  it 'user is following a tag' do
+    TagFollowing.user_is_following?(alice, @tag.name).should be_true
+  end
+
+  it 'user not following a tag' do
+    TagFollowing.user_is_following?(bob, @tag.name).should be_false
+  end
+  
 end