lazysmallcheck is a demand-driven testing library for Haskell programs. It requires fewer test cases to verify properties for inputs for a depth. It is now available on Fedora. Install it using:

 $ sudo yum install ghc-lazysmallcheck-devel

The depthCheck function lists the number of fewer tests required at a given depth. For example:

import Test.LazySmallCheck
import System

type Set a = [a]

empty :: Set a
empty = []

insert :: Ord a => a -> Set a -> Set a
insert a [] = [a]
insert a (x:xs)
  | a < x = a:x:xs
  | a > x = x:insert a xs
  | a == x = x:xs

set :: Ord a => [a] -> Set a
set = foldr insert Main.empty

ordered [] = True
ordered [x] = True
ordered (x:y:zs) = x <= y && ordered (y:zs)

allDiff [] = True
allDiff (x:xs) = x `notElem` xs && allDiff xs

isSet s = ordered s && allDiff s

-- Properties

infixr 0 -->
False --> _ = True
True --> x = x

prop_insertSet :: (Char, Set Char) -> Bool
prop_insertSet (c, s) = ordered s --> ordered (insert c s)

main = do
        [d] <- getArgs
        depthCheck (read d) prop_insertSet

You can compile and run it using:

~~~~ {.shell} $ ghc –make ListSet.hs [1 of 1] Compiling Main ( ListSet.hs, ListSet.o ) Linking ListSet …

$ ./ListSet 2 OK, required 23 tests at depth 2 ~~~~