deleting a forum topic should delete its posts

app/models/forum_topic.rb

@@ -2,7 +2,7 @@ class ForumTopic < ActiveRecord::Base
   attr_accessible :title, :original_post_attributes
   belongs_to :creator, :class_name => "User"
   belongs_to :updater, :class_name => "User"
-  has_many :posts, :class_name => "ForumPost", :order => "forum_posts.id asc", :foreign_key => "topic_id"
+  has_many :posts, :class_name => "ForumPost", :order => "forum_posts.id asc", :foreign_key => "topic_id", :dependent => :destroy
   has_one :original_post, :class_name => "ForumPost", :order => "forum_posts.id asc", :foreign_key => "topic_id"
   before_validation :initialize_creator, :on => :create
   before_validation :initialize_updater

test/functional/forum_topics_controller_test.rb

@@ -74,7 +74,16 @@ class ForumTopicsControllerTest < ActionController::TestCase
     end
     
     context "destroy action" do
+      setup do
+        @post = Factory.create(:forum_post, :topic_id => @forum_topic.id)
+      end
       
+      should "destroy the topic and any associated posts" do
+        assert_difference(["ForumPost.count", "ForumTopic.count"], -1) do
+          post :destroy, {:id => @forum_topic.id}, {:user_id => @user.id}
+        end
+        assert_redirected_to(forum_topics_path)
+      end
     end
   end
 end

test/unit/forum_topic_test.rb

@@ -42,5 +42,19 @@ class ForumTopicTest < ActiveSupport::TestCase
         assert_equal(@second_user.id, @topic.updater_id)
       end
     end
+    
+    context "with multiple posts that has been deleted" do
+      setup do
+        5.times do
+          Factory.create(:forum_post, :topic_id => @topic.id)
+        end
+      end
+      
+      should "delete any associated posts" do
+        assert_difference("ForumPost.count", -5) do
+          @topic.destroy
+        end
+      end
+    end
   end
 end