quickcheck-testing

-- In .cabal:
build-depends: QuickCheck >= 2.18

-- In stack.yaml: add 'QuickCheck' to extra-deps if not in resolver

// build.sbt
libraryDependencies += "org.scalacheck" %% "scalacheck" % "1.18.0" % Test

// For ScalaTest integration:
libraryDependencies += "org.scalatest" %% "scalatest-propspec" % "3.2.18" % Test

import Test.QuickCheck

prop_reverseInvolutive :: [Int] -> Bool
prop_reverseInvolutive xs = reverse (reverse xs) == xs

main :: IO ()
main = quickCheck prop_reverseInvolutive

ghci> quickCheck prop_reverseInvolutive
+++ OK, passed 100 tests.

data User = User { userId :: Int, userEmail :: String, userAge :: Int }
  deriving (Show, Eq)

instance Arbitrary User where
  arbitrary = do
    uid <- arbitrary `suchThat` (> 0)
    name <- listOf1 (elements ['a'..'z'])
    age <- choose (18, 100)
    return $ User uid (name ++ "@example.com") age

  shrink (User i e a) =
    [ User i' e a | i' <- shrink i, i' > 0 ] ++
    [ User i e a' | a' <- shrink a, a' >= 18, a' <= 100 ]

-- Conditional property: discard cases where xs is empty
prop_headOfNonEmpty :: [Int] -> Property
prop_headOfNonEmpty xs = not (null xs) ==> head xs == xs !! 0

import org.scalacheck._
import org.scalacheck.Prop.forAll

object UserSpecification extends Properties("User") {

  implicit val userGen: Arbitrary[User] = Arbitrary {
    for {
      id <- Gen.posNum[Int]
      name <- Gen.alphaLowerStr.suchThat(_.length >= 3)
      age <- Gen.choose(18, 100)
    } yield User(id, s"$name@example.com", age)
  }

  property("json round-trip") = forAll { (u: User) =>
    val json = encode(u)
    decode[User](json) == Right(u)
  }

  property("sorted list stays sorted") = forAll { (xs: List[Int]) =>
    val sorted = xs.sorted
    sorted == sorted.sorted
  }
}

import Test.QuickCheck

main = quickCheckWith (stdArgs { maxSuccess = 1000, maxSize = 100 }) prop_X
-- or:
quickCheckWith (stdArgs { maxSuccess = 100, maxSize = 50, maxDiscardRatio = 10 }) prop_X

import org.scalacheck.Test
import org.scalacheck.Prop

val params = Test.Parameters.default
  .withMinSuccessfulTests(1000)
  .withMaxDiscardRatio(10.0f)

cabal test

sbt test

quickCheckWith (stdArgs { replay = Just (mkQCGen 42, 0) }) prop_X

val params = Test.Parameters.default.withInitialSeed(rng.Seed(42L))