Adds test to check that circular preloading does not modify Model.unscoped (as described in #5667)

activerecord/test/cases/associations/eager_test.rb

@@ -1174,6 +1174,12 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_equal Comment.find(1), Comment.preload(:post => :comments).scoping { Comment.find(1) }
   end
 
+  test "circular preload does not modify unscoped" do
+    expected = FirstPost.unscoped.find(2)
+    FirstPost.preload(:comments => :first_post).find(1)
+    assert_equal expected, FirstPost.unscoped.find(2)
+  end
+
   test "preload ignores the scoping" do
     assert_equal(
       Comment.find(1).post,

activerecord/test/cases/relations_test.rb

@@ -1099,10 +1099,6 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal 'honda', FastCar.unscoped { FastCar.order_using_old_style.limit(1).first.name}
   end
 
-  def test_unscoped_relation_clones
-    assert_not_equal CoolCar.unscoped.object_id, CoolCar.unscoped.object_id
-  end
-
   def test_intersection_with_array
     relation = Author.where(:name => "David")
     rails_author = relation.first

activerecord/test/models/comment.rb

@@ -9,6 +9,8 @@ class Comment < ActiveRecord::Base
   belongs_to :post, :counter_cache => true
   has_many :ratings
 
+  belongs_to :first_post, :foreign_key => :post_id
+
   has_many :children, :class_name => 'Comment', :foreign_key => :parent_id
   belongs_to :parent, :class_name => 'Comment', :counter_cache => :children_count