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Hedgehog

You can use sandwich-hedgehog (provided as a separate package) to easily integrate integrate Hedgehog tests into the test tree.

Haddocks can be found here.

Usage​

To use sandwich-hedgehog, just add the package to your project. Then, introduce a Hedgehog argument context using introduceHedgehog. Now you can start writing props as test nodes using the prop function. For example:

https://github.com/codedownio/sandwich/blob/master/demos/demo-hedgehog/app/Main.hs
import Hedgehog
import qualified Hedgehog.Gen as Gen
import qualified Hedgehog.Range as Range

hedgehogDemo :: TopSpec
hedgehogDemo = describe "Hedgehog tests" $ introduceHedgehog $ do
  prop "List reversal" $ do
    xs <- forAll $ Gen.list (Range.linear 0 100) Gen.alpha
    reverse (reverse xs) === xs

  prop "Failing list reversal" $ do
    xs <- forAll $ Gen.list (Range.linear 0 100) Gen.alpha
    reverse xs === xs

Modifying the parameters​

If you use introduceHedgehog', you can pass your own value for the HedgehogParams.

If you want to modify the already-introduced arguments in a test tree, we provide the modifyArgs function, as well as helpers like modifySeed, modifySize, etc. These are modelled directly after HSpec's Test.Hspec.Hedgehog.

Controlling Hedgehog parameters with command line args​

If you use the introduceHedgehogCommandLineOptions family of functions, then some Hedgehog parameters can be controlled via the command line. To see the valid options, run Sandwich with --print-hedgehog-flags.

Usage: demo [--hedgehog-seed STRING] [--hedgehog-size INT]
            [--hedgehog-discard-limit INT]
            [--hedgehog-shrink-limit INT]
            [--hedgehog-shrink-retries INT] [--hedgehog-confidence INT]

Available options:
  --hedgehog-seed STRING   Seed as a tuple (a, b)
  --hedgehog-size INT      Size of the randomly-generated data
  --hedgehog-discard-limit INT
                           The number of times a property is allowed to discard
                           before the test runner gives up
  --hedgehog-shrink-limit INT
                           The number of times a property is allowed to shrink
                           before the test runner gives up and prints the
                           counterexample
  --hedgehog-shrink-retries INT
                           The number of times to re-run a test during shrinking
  --hedgehog-confidence INT
                           The acceptable occurrence of false positives

Demo​

A demo is provided in the Sandwich repo.

git clone git@github.com:codedownio/sandwich.git
cd sandwich
stack run demo-hedgehog -- --tui