can no longer delete posts in locked forum topics

app/models/forum_post.rb

@@ -1,6 +1,6 @@
 class ForumPost < ActiveRecord::Base
   attr_accessible :body, :topic_id
-  attr_accessible :body, :topic_id, :as => [:admin, :moderator, :janitor]
+  attr_accessible :body, :topic_id, :is_locked, :is_sticky, :as => [:admin, :moderator, :janitor]
   belongs_to :creator, :class_name => "User"
   belongs_to :topic, :class_name => "ForumTopic"
   before_validation :initialize_creator, :on => :create
@@ -8,6 +8,7 @@ class ForumPost < ActiveRecord::Base
   after_save :update_topic_updated_at
   validates_presence_of :body, :creator_id
   validate :validate_topic_is_unlocked
+  before_destroy :validate_topic_is_unlocked
   scope :body_matches, lambda {|body| where(["forum_posts.text_index @@ plainto_tsquery(?)", body])}
   scope :for_user, lambda {|user_id| where("forum_posts.creator_id = ?", user_id)}
   search_methods :body_matches

test/unit/forum_post_test.rb

@@ -14,6 +14,25 @@ class ForumPostTest < ActiveSupport::TestCase
       CurrentUser.ip_addr = nil
     end
     
+    context "belonging to a locked topic" do
+      setup do
+        @post = Factory.create(:forum_post, :topic_id => @topic.id, :body => "zzz")
+        @topic.update_attribute(:is_locked, true)
+        @post.reload
+      end
+      
+      should "not be updateable" do
+        @post.update_attributes(:body => "xxx")
+        @post.reload
+        assert_equal("zzz", @post.body)
+      end
+      
+      should "not be deletable" do
+        @post.destroy
+        assert_equal(1, ForumPost.count)
+      end
+    end
+    
     should "update its parent when saved" do
       sleep 1
       original_topic_updated_at = @topic.updated_at