ErrorsTest.scala

import scala.concurrent.duration._
import scala.concurrent.{Await, Future}
import scala.concurrent.ExecutionContext.Implicits.global
import org.scalatest.FunSuite

class ErrorsTest extends FunSuite {
  test("Future can recover from error") {
    val numberFuture: Future[Int] = generateNumber()
    val addedFuture: Future[Int] = numberFuture.map(addThree).recover({
      case exception: IllegalStateException => -1
    })

    val added: Int = Await.result(addedFuture, 1 seconds)
    assert(added == -1)
  }

  private def generateNumber(): Future[Int] = Future {
    Thread.sleep(100)
    throw new IllegalStateException()
  }

  def addThree(value: Int): Int =
    value + 3
}