The current rating of a circuit breaker is usually stamped in the top of the switch handle itself. If not there when you remove the breaker the part number and rating should be on the side.
As for a breaker riveted to the cover of the panel that sounds like an after thought.
If you want to test a breaker just apply a load that is at least 90% of the rating. Breakers are designed to trip at 80% of rating. A toaster and a hair dryer is a crude way but should trip a 20 amp breaker.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles