hspecVariant

Spec for testing properties for variant types

{-# LANGUAGE TypeSynonymInstances #-}

type Natural = Integer

instance Variant Natural where
  invalid = do
    n <- arbitrary
    if (n<0) then return n else return ((-1)*(n+1))
  valid = do
    n <- arbitrary
    if (n>=0) then return n else return ((-1)*(n+1))

Test

main::IO ()
main = hspec $
  describe "Naturals" $
    propValid "succ" $
      \x -> succ (x::Natural) > 0