ScalaCheckで独自のGeneratorを作る ref: http://qiita.com/atsuya046/items/2ab7505336a9f892bc47

build.sbt

libraryDependencies += "org.scalacheck" %% "scalacheck" % "1.12.5" % "test"

file3.txt

$ sbt test
~
[info] + MyClass.calc: OK, passed 100 tests.
[info] Passed: Total 1, Failed 0, Errors 0, Passed 1
[success] Total time: 4 s, completed 2016/01/28 11:28:23

MyClass.scala

case class MyClass(number: Int, multiplier: Multiplier) {

  def calc: Int = {
    number * multiplier.number
  }
}

case class Multiplier(number: Int)

MyClassTest.scala

import org.scalacheck.{Arbitrary, Gen, Prop, Properties}

object MyClassTest extends Properties("MyClass") {

  // MultiplierのGenerator
  // -1000 ~ 1000のnumberを持つMultiplierを生成します
  val genMultiplier: Gen[Multiplier] = for {
    number <- Gen.chooseNum(-1000, 1000)
  } yield Multiplier(number)

  // MyClassのGenerator
  // -1000 ~ 1000のnumberとgenMultiplierで生成したMultiplierを持つMyClassを生成します
  val genMyClass: Gen[MyClass] = for {
    number <- Gen.chooseNum(-1000, 1000)
    multiplier <- genMultiplier
  } yield MyClass(number, multiplier)

  // Prop.forAllでMyClassの乱数を呼び出す際にArbitraryを定義
  implicit val arbMyClass = Arbitrary {genMyClass}

  // テストの実行
  // 100パターンのMyClassをランダムに生成してcalcの挙動を
  property("calc") = Prop.forAll{(myClass: MyClass) =>
    myClass.calc == myClass.number * myClass.multiplier.number
  }

}