> Suppose I tell you 3 + 2 = 5 and 2 + 3 = 5. Did you learn anything non-trivial about + from those two examples? Did you learn that x + y = y + x for all x and

> Suppose I tell you 3 + 2 = 5 and 2 + 3 = 5. Did you learn anything non-trivial about + from those two examples? Did you learn that x + y = y + x for all x and y or that x + (y + z) = (x + y) + z? You can sample as many points as you want and you'll still be no wiser as to how + behaves and how it interacts with * or that the implementation of + even respects any of those properties. If you're going to put in the effort to generate unit tests then why not go a bit further and formally verify the correct functionality? One could take the middle road and express commutativity, distributivity etc. through invariants and use a fuzzy testing tool to generate tests for it. Generating 100 tests sounds a lot better than a single handwritten one, though of course it's not as good as actually proving it for all inputs.