"Equal Justice Under Law" & Black Hood & Orange Jumpsuit, Outside The Third Guantanamo Hearing At the Supreme Court (Washington, DC)

I'm a student of government, but for the life of me cannot figure out the point of various "tests" when looking at legal cases. I know that these tests are used to derive some sort of logic for a decision given. A good example is the Lemon Test. But I still just can't seem to understand how one would apply those tests to more than one case. Thus, the likelihood of me ever being a lawyer in a field where almost everyone has a law degree is unlikely.