Do you really need that Diploma, Scarecrow?
Seriously, it's the skill and consistency that are important.
Study and practice as if you were going to take the test.
You can decide whether or not to take it after you are good enough to pass.
BTW. Knowing how to play or teach winning tennis does not qualify one to be a good racquet tech, either.
I also repair and service bikes, but I haven't ridden in years.
I play guitar and bass as well and I know when to bring them to a luthier.