Merge pull request #15545 from zuhao/refactor_actionpack_assert_select_test

Restore test deliveries for ActionMailer.

actionpack/test/controller/assert_select_test.rb

@@ -56,13 +56,16 @@ def xml()
 
   def setup
     super
+    @old_delivery_method = ActionMailer::Base.delivery_method
+    @old_perform_deliveries = ActionMailer::Base.perform_deliveries
     ActionMailer::Base.delivery_method = :test
     ActionMailer::Base.perform_deliveries = true
-    ActionMailer::Base.deliveries = []
   end
 
   def teardown
     super
+    ActionMailer::Base.delivery_method = @old_delivery_method
+    ActionMailer::Base.perform_deliveries = @old_perform_deliveries
     ActionMailer::Base.deliveries.clear
   end