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exercism fetch haskell nth-prime

test/Tests.hs

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{-# 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 Prime (nth)

main :: IO ()
main = hspecWith defaultConfig {configFastFail = True} specs

specs :: Spec
specs = describe "nth" $ for_ cases test
  where

    test Case{..} = it description assertion
      where
        assertion = nth (fromIntegral input) `shouldBe` expected

data Case = Case { description :: String
                 , input       :: Integer
                 , expected    :: Maybe Integer
                 }

cases :: [Case]
cases = [ Case { description = "first prime"
               , input       = 1
               , expected    = Just 2
               }
        , Case { description = "second prime"
               , input       = 2
               , expected    = Just 3
               }
        , Case { description = "sixth prime"
               , input       = 6
               , expected    = Just 13
               }
        , Case { description = "big prime"
               , input       = 10001
               , expected    = Just 104743
               }
        , Case { description = "there is no zeroth prime"
               , input       = 0
               , expected    = Nothing
               }
        ]