[Hedgehog](http://hedgehog.qa/) automatically generates a comprehensive array of test cases, exercising your software in ways human testers would never imagine. Generate hundreds of test cases automatically, exposing even the most insidious of corner cases. Failures are automatically simplified, giving developers coherent, intelligible error messages. ## Features - Integrated shrinking, shrinks obey invariants by construction. - Abstract state machine testing. - Generators allow monadic effects. - Range combinators for full control over the scope of generated numbers and collections. - Equality and roundtrip assertions show a diff instead of the two inequal values. - Template Haskell test runner which executes properties concurrently. ## Example The main module, [Hedgehog][haddock-hedgehog], includes almost everything you need to get started writing property tests with Hedgehog. It is designed to be used alongside [Hedgehog.Gen][haddock-hedgehog-gen] and [Hedgehog.Range][haddock-hedgehog-range] which should be imported qualified. You also need to enable Template Haskell so the Hedgehog test runner can find your properties. ```hs {-# LANGUAGE TemplateHaskell #-} import Hedgehog import qualified Hedgehog.Gen as Gen import qualified Hedgehog.Range as Range ``` Once you have your imports set up, you can write a simple property: ```hs prop_reverse :: Property prop_reverse = property $ do xs <- forAll $ Gen.list (Range.linear 0 100) Gen.alpha reverse (reverse xs) === xs ``` And add the Template Haskell splice which will discover your properties: ```hs tests :: IO Bool tests = checkParallel $$(discover) ``` If you prefer to avoid macros, you can specify the group of properties to run manually instead: ```hs {-# LANGUAGE OverloadedStrings #-} tests :: IO Bool tests = checkParallel $ Group "Test.Example" [ ("prop_reverse", prop_reverse) ] ``` You can then load the module in GHCi, and run it: ``` λ tests ━━━ Test.Example ━━━ ✓ prop_reverse passed 100 tests. ```