I am a Haskell beginner, using GHC 6.4.1. Suppose I have a function, tt, say, which may call error. For the purposes of testing tt, I'd like to be able to catch the error string and assert that it matches the expected error string. Is HUnit or QuickCheck (or either) the appropriate tool for this sort of testing? I managed to get it working with HUnit, but it's horribly kludgy mainly because I'm yet to grok monads. The little test program below demonstrates my question outside of HUnit: import Control.Exception tt :: String -> Int tt s = error ("hi error '" ++ s ++ "'") -- tt s = read s ttWrap :: String -> IO String ttWrap x = do let r = tt x -- comment out next line, error string not caught putStr (show r) return (show r) ttWrap2 :: IO String ttWrap2 = do res <- tryJust errorCalls (ttWrap "123") case res of Right r -> return (show r) Left r -> return r main = do x <- ttWrap2 putStrLn ("caught:" ++ x) y <- ttWrap2 putStrLn ("caught:" ++ y) When you run the above test program, it does indeed catch the error string thrown by the tt function (and prints it out in main). However, if you comment out the putStr line as shown in the comment above, it no longer catches the error string, but dies instead. Why? I'm sure there is a cleaner way to achieve what I'm trying to do and I'd appreciate advice on the best way to do this. Thanks, /-\ Send instant messages to your online friends http://au.messenger.yahoo.com