PropertyBasedTestingExample.scala

package basics

import org.scalatest.matchers.should.Matchers
import org.scalatest.wordspec.AnyWordSpec
import org.scalatestplus.scalacheck.ScalaCheckDrivenPropertyChecks
import org.scalacheck.Gen
import org.scalacheck.Arbitrary

class MathSpec extends AnyWordSpec with Matchers with ScalaCheckDrivenPropertyChecks {

  def absolute(n: Int): Int =
    if (n < 0) -n else n

  "absolute" should {
    "turn a negative into a positive" in {
      val negatives = Gen.negNum[Int]

      forAll(negatives) { (n: Int) =>
        absolute(n) should be > 0
      }
    }

    "leave a positive as-is" in {
      val positives = Gen.negNum[Int]

      forAll(positives) { (n: Int) =>
        absolute(n) should be(n)
      }
    }
  }

  def isEven(num: Int): Boolean =
    num % 2 == 0

  "isEven" should {
    "recognise an even number" in {
      val numbers = Arbitrary.arbitrary[Int]

      forAll(numbers) { (n: Int) =>
        isEven(2 * n) should be(true)
      }
    }

    "recognise an odd number" in {
      val numbers = Arbitrary.arbitrary[Int]

      forAll(numbers) { (n: Int) =>
        isEven(2 * n - 1) should be(false)
      }
    }
  }

}