Prefix ActionView::Base private methods with an underscore

actionpack/lib/action_controller/test_process.rb

@@ -218,7 +218,7 @@ module ActionController #:nodoc:
     # Returns the template of the file which was used to
     # render this response (or nil)
     def rendered_template
-      template._first_render
+      template.send(:_first_render)
     end
 
     # A shortcut to the flash. Returns an empty hash if no session flash exists.