Hello Klaus,

if you are running the Google Mobile firendly test AFTER an upgrade to Joomla 3.4, the templates folder will be still blocked in the robots.txt.

if you are using JSitemap Pro you can easily edit the robots.txt and remove the Disallow rule for the 'templates' folder, allowing the google bot to access properly resources also for the mobile friendly test. keep in mind that after editing it Google will need some days to refresh the robots.
In the attachment click to open the edit screen of the robots.txt, remove the highlighted line for 'templates' and save.

best regards

John