How does one professionally test ignition components? What special tools are involved? I know there are many ways to go about it as far as assuming and replacing, but that gets expensive and frustrating. how does one do a proper check of each component? Do you need a special tool like a mercotronic tester? or will a multimeter do the trick. I want to learn how to diagnose problems the right way, and avoid replacing expensive parts with nothing but a guess.

Thanks