Add test verifying that you can only sort ARs of the same type

Author: David Heinemeier Hansson

activerecord/test/cases/base_test.rb

@@ -554,13 +554,19 @@ def test_hashing
     assert_equal [ Topic.find(1) ], [ Topic.find(2).topic ] & [ Topic.find(1) ]
   end
 
-  def test_comparison
+  def test_successful_comparison_of_like_class_records
     topic_1 = Topic.create!
     topic_2 = Topic.create!
 
     assert_equal [topic_2, topic_1].sort, [topic_1, topic_2]
   end
 
+  def test_failed_comparison_of_unlike_class_records
+    assert_raises ArgumentError do
+      [ topics(:first), posts(:welcome) ].sort
+    end
+  end
+
   def test_create_without_prepared_statement
     topic = Topic.connection.unprepared_statement do
       Topic.create(:title => 'foo')