...and remember to make tests that don't confirm your model. If the set is 2, 4, 8, and your model is "powers of two", then, sure test 16, but also test 1, 3, 6, 0.5, 0.1 (maybe the correct model is "also 2 to the power 0" or "two to any integer, including negatives" or "all even numbers" or "any integer" - or something else).