For my testing, I would like to generate arbitrary random functions of type String => Boolean.
Is it possible to do that using ScalaCheck?
Yes, just like you'd generate arbitrary values of other types:
import org.scalacheck._
// Int instead of Boolean to better see that it is a function
val arb = implicitly[Arbitrary[String => Int]].arbitrary.sample.get
println(arb("a"))
println(arb("a")) // same
println(arb("b"))
because there is an implicit Cogen[String] and an Arbitrary[Boolean]. Cogen is not documented in the User Guide, but it's equivalent to QuickCheck's CoArbitrary which is explained in https://kseo.github.io/posts/2016-12-14-how-quick-check-generate-random-functions.html and https://begriffs.com/posts/2017-01-14-design-use-quickcheck.html (under "CoArbitrary and Gen (a -> b)").
Is it possible then to generate arbitrary function from a random case class then? For example
case class File(name: Str, size:Long)
It should be enough to define a Cogen[File]. Either manually:
implicit val cogenFile: Cogen[File] = Cogen {
(seed: Seed, file: File) => Cogen.perturbPair(seed, (file.name, file.size))
}
Slightly more code, but generalizes to more than 2 fields:
implicit val cogenFile: Cogen[File] = Cogen { (seed: Seed, file: File) =>
val seed1 = Cogen.perturb(seed, file.name)
Cogen.perturb(seed1, file.size)
}
Or automatically using scalacheck-shapeless:
implicit val cogenFile: Cogen[File] = MkCogen[File].cogen