gistfile1.txt

{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
module Spec (main) where
import           Test.HUnit
import           System.Process
import           System.IO

subprocess = concat $
  [ "module Main where\n"
  , "import System.IO\n"
  , "main = do\n"
  , "  hPutStr stderr \"foo\"\n"
  , "  hFlush stderr\n"
  , "  hPutStrLn stdout \"bar\"\n"
  , "  hFlush stdout\n"
  ]

main = runTestTT $ TestCase $ do
  (Just hin, Just hout, Nothing, _) <-
    createProcess $ (shell "runhaskell 2>&1") {
        std_in = CreatePipe
      , std_out = CreatePipe
      , std_err = Inherit
    }
  hPutStrLn hin subprocess
  hClose hin
  line <- hGetLine hout
  line @?= "foobar"