to expand on c00p3r's comment, you can test whatever you want to test in a unit test. basically you are testing the response of a "unit." The unit can be whatev

to expand on c00p3r's comment, you can test whatever you want to test in a unit test. basically you are testing the response of a "unit." The unit can be whatever you feel like but it it typically a class of some sort depending on the language. Typically you test the extremes of inputs, invalid inputs and some valid inputs inside the extremes. It's hard to write comprehensive tests but once you write them you can keep adding to them when you find a new bug. Just remember that nothing is infalible.