Snippets.scala

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

class Snippets extends FunSuite {

  test("Promise can be fulfilled") {
    val numberPromise = Promise[Int]()
    val addedFuture = addThree(numberPromise.future)
    assert(addedFuture.isCompleted == false)

    numberPromise.success(7)

    val added = Await.result(addedFuture, 1 seconds)
    assert(added == 10)
  }

  def addThree(value: Future[Int]): Future[Int] = 
    value.map(a => a + 3)
}