QCFail.hs

QCFail.hs

import Data.Either (isLeft)
import Control.Exception (try, evaluate, SomeException)
import Test.QuickCheck (Property, quickCheck)
import Test.QuickCheck.Monadic (monadicIO, run, assert)

isFailure :: a -> IO Bool
isFailure = fmap isLeft . tryEval
  where
    tryEval :: a -> IO (Either SomeException a)
    tryEval = try . evaluate

prop_empty_list :: Int -> Property
prop_empty_list idx = monadicIO (run (isFailure ([] !! idx)) >>= assert)

prop_unexpected_success :: Int -> Property
prop_unexpected_success idx = monadicIO (run (isFailure ([()] !! idx)) >>= assert)

main :: IO ()
main = mapM_ quickCheck [ prop_empty_list, prop_unexpected_success ]