Merge pull request #6605 from amatsuda/ar_merge_association_test

a test case that ensures AR::Relation#merge can merge associations

activerecord/test/cases/relations_test.rb

@@ -695,6 +695,14 @@ def test_relation_merging_with_joins
     assert_equal 1, comments.count
   end
 
+  def test_relation_merging_with_association
+    assert_queries(2) do  # one for loading post, and another one merged query
+      post = Post.where(:body => 'Such a lovely day').first
+      comments = Comment.where(:body => 'Thank you for the welcome').merge(post.comments)
+      assert_equal 1, comments.count
+    end
+  end
+
   def test_count
     posts = Post.scoped