content: {-# OPTIONS_GHC -fno-warn-type-defaults #-}
  {-# LANGUAGE RecordWildCards #-}
  
  import Data.Foldable     (for_)
  import Test.Hspec        (Spec, describe, it, shouldBe)
  import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)
  
  import CollatzConjecture (collatz)
  
  main :: IO ()
  main = hspecWith defaultConfig {configFastFail = True} specs
  
  specs :: Spec
  specs = describe "collatz" $ for_ cases test
    where
  
      test Case{..} = it description assertion
        where
          assertion = collatz number `shouldBe` expected
  
  
  data Case = Case { description :: String
                   , number      :: Integer
                   , expected    :: Maybe Integer
                   }
  
  cases :: [Case]
  cases = [ Case { description = "zero steps for one"
                 , number      = 1
                 , expected    = Just 0
                 }
          , Case { description = "divide if even"
                 , number      = 16
                 , expected    = Just 4
                 }
          , Case { description = "even and odd steps"
                 , number      = 12
                 , expected    = Just 9
                 }
          , Case { description = "Large number of even and odd steps"
                 , number      = 1000000
                 , expected    = Just 152
                 }
          , Case { description = "zero is an error"
                 , number      = 0
                 , expected    = Nothing
                 }
          , Case { description = "negative value is an error"
                 , number      = -15
                 , expected    = Nothing
                 }
          ]
  