Тестирование скала-приложений

package chapter01

object MyModule {
  def abs(n: Int): Int =
    if (n < 0) -n
    else n

  private def formatAbs(x: Int): String = {
    val msg = "The absolute value of %d is %d"
    msg.format(x, abs(x))
  }

  def main(args: Array[String]): Unit =
    println(formatAbs(-42))
}

import org.scalatest._
import org.scalatest.PrivateMethodTester._

import chapter01.MyModule

class chapter01Spec extends FlatSpec with Matchers {
  "Absolute value of neg integers" should "return correct values" in {
    MyModule.abs(-42) should be(42)
    MyModule.abs(-1234567890) should be(1234567890)
    MyModule.abs(42) should be(42)
  }

  "formatAbs" should "return correct string" in {
    val formatAbs = PrivateMethod[String]('formatAbs)
    MyModule invokePrivate formatAbs(-42) should be("The absolute value of -42 is 42")
  }
....

....
  "main" should "return Unit type" in {
    val formatAbs = PrivateMethod[String]('formatAbs)
    val a = MyModule.main(new Array[String](0))
    val b = MyModule invokePrivate formatAbs(-42)
    a should be (println(b))}}