The dealers don't care about the generalized tests. They are concerned with specific models and usually provide the special instructions/instruction regarding their models. That's good and bad.

The Kookawinga models you work on daily might use the same principle of operation but the Bullsamingo car has a completely different way to achieve the same results.

" A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.

-Robert A. Heinlein"

You want a good field to go into mechanic-wise? Try fleet maintenance. Usually a salaried position, steady work, benefits and you are employed by a larger company which lessens the risk of your job disappearing at the owner's whim.

You WILL learn everything there is to know about full and complete maintenance of vehicles. Much, much more than you ever wanted to know. Bumper to bumper, tires to the sky, EVERYTHING becomes your problem.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now