Eugene Kirpichov wrote:
Use QuickCheck.
Also use SmallCheck or lazy SmallCheck. All of these are automatic tools that allow you to specify laws[1] and automatically generate values for testing the law. QuickCheck generates values randomly, which can be useful but is very often insufficient. Both versions of SmallCheck do exhaustive search of all values down to a bounded "depth" (lazy SmallCheck can often search deeper and faster). If you want to have decent assurances of correctness then use (lazy) SmallCheck. If you're dealing with a really branchy type which makes it prohibitive to search to any reasonable depth, then use QuickCheck in addition. Occasionally QuickCheck can be good for ferreting out really obscure corner cases, but SmallCheck is much better about guaranteeing you get all the basic cases. [1] e.g. prop_compare a b = compare a b == negateOrdering (compare b a) where negateOrdering LT = GT negateOrdering EQ = EQ negateOrdering GT = LT -- Live well, ~wren