Add order to tests that rely on db ordering, to fix failing tests on pg

Also skip persistente tests related to UPDATE + ORDER BY for postgresql

PostgreSQL does not support updates with order by, and these tests are
failing randomly depending on the fixture loading order now.

1 files changed, 1 insertions, 1 deletions

diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 5e0caf5fce..bf2807c384 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -674,7 +674,7 @@ class RelationTest < ActiveRecord::TestCase
   def test_relation_merging_with_preload
     ActiveRecord::IdentityMap.without do
       [Post.scoped.merge(Post.preload(:author)), Post.preload(:author).merge(Post.scoped)].each do |posts|
-        assert_queries(2) { assert posts.first.author }
+        assert_queries(2) { assert posts.order(:id).first.author }
       end
     end
   end