But how would you quantify the amount of learning that you've actually retained? Would it not be through some sort of question-answer based system on the material that you've covered, and using a weighted scale for each question depending on the difficulty of the question and how you applied the concepts?

As much as I enjoy learning about computers and circuits in class, how would I actually know I understood how they all interact with each other something without testing myself?

Acing an exam easily is a pretty good indication that you've learned the subject material fairly well.