[tikhonj]

Yes, static typing is not enough. Which is why a good statically typed language like Haskell also has great testing facilities. So you don't just write well typed code, but you also write unit tests (HUnit) and property-based tests (QuickCheck). The really neat bit is that static typing actually makes writing tests easier--QuickCheck is much easier to use in Haskell than it would be in some dynamically typed language.

[Dn_Ab]

QuickCheck is great and can be found in many languages - dynamic and static alike - nowadays. Another tool that is currently unique to Haskell and is easier to write tests for is Lazy/SmallCheck. SmallCheck shines in the left long tail of failure. Its core idea is based on a powerful principle: "If a program does not fail in any simple case, it hardly ever fails in any case."[]

So SmallCheck works exhaustively to find a minimal counterexample within some depth bound. This makes sense - when trying to characterize a structure for failure (or anything) you can rarely do better than the simplest explanation. However, when the problem lies in larger examples SmallCheck fails where QuickCheck catches a result so something like Type Check -> SmallCheck -> QuickCheck -> probably ok.

[] http://www.cs.york.ac.uk/fp/smallcheck/ documentation

[gtani]

and the guarantees (both random and exhaustive testing) for GenCheck

http://permalink.gmane.org/gmane.comp.lang.haskell.general/1...

[tikhonj]

Quickcheck exists in a bunch of different languages, but Haskell's type system makes it easier to use and implement because it can rely on type information to figure out which generator to use for any given input.