Reusable specifications

(similar in spirit to checkers)

Check Monoid laws

shouldSatisfyMonoidLaws can be used to specify, that a given type should satisfy the Monoid laws.

-- file Spec.hs
import Test.Hspec
import Test.Hspec.Laws

main :: IO ()
main = hspec $ do
  describe "List as a Monoid" $
    shouldSatisfyMonoidLaws (undefined :: [Int])

Running this produces a nice spec.

$ runhaskell Spec.hs

List as a Monoid
  mempty
    - is a left identity
    - is a right identity

  mappend
    - is associative

Finished in 0.1142 seconds
3 examples, 0 failures