embracing-nondeterminism-code/src/test/scala/green/thisfieldwas/embracingnondeterminism/stdlib/StringSpec.scala

package green.thisfieldwas.embracingnondeterminism.stdlib

import green.thisfieldwas.embracingnondeterminism.data.{Monoid, MonoidLaws, SemigroupLaws}
import green.thisfieldwas.embracingnondeterminism.util.Laws
import org.scalacheck.{Arbitrary, Gen}

/** Proves that Scala's String conforms to a Semigroup and Monoid.
  */
class StringSpec extends Laws with SemigroupLaws with MonoidLaws {

  implicit val arbitraryString: Arbitrary[String] = Arbitrary {
    for {
      length <- Gen.sized(Gen.choose(0, _))
      string <- Gen.stringOfN(length, Gen.asciiChar)
    } yield string
  }

  /** String forms a Semigroup under concatenation and a Monoid with an identity
    * value of an empty string "".
    */
  implicit val stringMonoid: Monoid[String] = new Monoid[String] {

    override def empty: String = ""

    override def combine(left: String, right: String): String = left + right
  }

  checkSemigroupLaws[String]()
  checkMonoidLaws[String]()
}