  Divisibility tests are algorithms that can quickly decide if one integer is
divisible by another. There are many tests but most are either of the trimming
or summing variety. Our goals are to present Zbikowski's family of trimming
tests as one test and to unify the trimming and summing tests. We do the latter
by showing, first, that the most effective summing tests, due to Khare, can be
derived directly from the Zbikowski's test and, second, that the best known
summing tests - the binomial tests - can be derived from an adapted form of
Zbikowski's tests. We introduce the notion of stacking, the claim that a six
year old would always choose 10 pennies over a dime, and use only basic
divisibility properties to achieve our goals.
