Generating arbitrary A => Date with scalacheck

Question

I'm running in an odd issue with scalacheck 1.13.3: arbitrary instances of A => java.util.Date generate different values depending on the time they are called.

Here's a concrete, reproducible example:

import org.scalatest.FunSuite
import org.scalatest.prop.GeneratorDrivenPropertyChecks
import java.util.Date
import org.scalacheck._

class Repr extends FunSuite with GeneratorDrivenPropertyChecks {
  implicit val cogenDate: Cogen[Date] = Cogen(_.getTime)

  test("reproduce") {
    forAll { (s: String, g: String => Date) =>
      val d1 = g(s)
      Thread.sleep(100)
      val d2 = g(s)

      assert(d1 === d2)
    }
  }
}

This fails. Printing the actual values of d1 and d2 shows that the dates are indeed different, with a difference of between 100 and 103 ms.

I would guess that the problem comes from my Cogen instance, but I must admit I don't understand why.

Answer 1

This turns out to be a regression in scalacheck 1.13.3, as discussed in the project's gitter channel. An issue was opened.