To my best knowledge..... The FAA doesn't require task proficiency tests for licensed mechanics on the line or hangar.
Proficiency is shown during A&P school and certain tasks can be asked to be performed while doing the oral and practical after school has been completed.
The A&P license can be thought of as a license to "learn". There is no way all aspects of aircraft maintenance can be taught at school. Mechanics tend to gravitate towards areas that they enjoy. Sheet-metal and structures being one area. I have no experience with sheet-metal and if an FAA representative asked me to do that job, I would fail.
There is also a big difference in line work vs. hangar. In the hanger, big jobs like flight control and gear changes occur regularly. Rigging is another major task in the hangar. Flight-line work requires the proficiency in aircraft systems as a whole. "Receive it, fix it, get it out of town".
FAA reps can certainly watch you perform your work and write you up if manuals aren't followed and procedures not completed. Your license can be pulled if you screw up.
I guess the EASA can pull your certification on one aircraft type. With the FAA..... they can pull it for "everything". No license, no job. Although there are steps for retraining to get your certification back.