scala - 既存のキーを持つ NoSuchElementException

Question

建物のクラス:

class Building(val name: String, val skill: String, @volatile var workHours: Int) {

  var workers = new HashMap[Artisan, Int]()

  def doWork(worker: Artisan): Boolean = {
    ...
    workers.get(worker) match {
      case Some(i: Int) =>
        worker.cash += i
        true
      case None => false
    }
    ...
  }

職人クラス:

class Artisan(val skill: String, city: City) extends Player(skill, city) {
  var assignment = new Building("Empty", "", 0)

  def doWork() {
    if ( !assignment.doWork(this) )
    ...
  }

  def canEqual(other: Any): Boolean = other.isInstanceOf[Artisan]

  override def equals(other: Any): Boolean = other match {
    case that: Artisan =>
      (that canEqual this) &&
        assignment == that.assignment &&
        skill == that.skill
    case _ => false
  }

  override def hashCode(): Int = {
    val state = Seq(assignment, skill)
    state.map(_.hashCode()).foldLeft(0)((a, b) => 31 * a + b)
  }
}

テストケース：

@Test
def testIncome() {
  val building = new Building("Bakery", "Builder", 10)
  building.setSallery(100, player)  // add player to building hashmap
  player.assignment = building
  player.doWork()
  assertEquals("Should earn 100", player.cash, 100)
}

出力：

Negative test case

このコードが実際にこのエラーをどのように提供するのかわかりません。要素が存在しない場合、コードが false を返す必要がある場合。プログラムをデバッグすると Artisan オブジェクトがハッシュマップに追加されるので、失敗する理由がわかりません。