# Pastebin MPAt1waK
#!/usr/bin/env stack
-- stack --resolver lts-18.0 script

{-# LANGUAGE DerivingStrategies         #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE NamedFieldPuns             #-}

import           Test.Hspec
import           Test.QuickCheck hiding (Result)

data Result = One | NotOne deriving (Eq, Show)

myFunc :: [Int] -> Result
myFunc xs = if 1 `elem` xs then One else NotOne

main :: IO ()
main = hspec spec

spec :: Spec
spec = describe "myFunc" $ do
  it "is 'One' when list contains 1"
    $ property
    $ \ContainsOne { unContainsOne } -> myFunc unContainsOne `shouldBe` One

newtype ContainsOne = ContainsOne
  { unContainsOne :: [Int]
  }
  deriving newtype Show

instance Arbitrary ContainsOne where
  arbitrary = do
    list <- arbitrary
    let xs = 1 : list
    pure $ ContainsOne xs