Ask is @controller is defined to avoid warning.

actionpack/lib/action_dispatch/testing/assertions/routing.rb

@@ -171,7 +171,7 @@ def with_routing
 
       # ROUTES TODO: These assertions should really work in an integration context
       def method_missing(selector, *args, &block)
-        if @controller && @routes && @routes.named_routes.helpers.include?(selector)
+        if defined?(@controller) && @controller && @routes && @routes.named_routes.helpers.include?(selector)
           @controller.send(selector, *args, &block)
         else
           super