A person who is a good test-taker... may or may not be a good tech.
And a lousy test-taker might be a GREAT tech, or a poor one.
Mechanical understanding is something one learns from years of working with their hands, along with a natural knack for mechanical things... Same with electrical things. IMO there is really no way to test this... one just has to have the knack and experience.
Licensing, in reality, is not about ability... it is about limiting competition and govt collecting fees (mostly govt fees). Nothing more. There are as many hacks with licenses as without.
I happen to have mechanical aptitude and am a good test taker.
Everything else is up for debate. Licensing is restraint of trade plain and simple.