test("Test empty tree 'Contains'") {

    // behind the scene this on create a node actor - follow props: Props(classOf[BinaryTreeNode],  elem, initiallyRemoved)
    val testNode = system.actorOf(BinaryTreeNode.props(0, true))

    testNode ! Contains(testActor, id = 1, 0)
    expectMsg(ContainsResult(1, false))
  }

  test("Test empty tree 'Insert'") {
    val testNode = system.actorOf(BinaryTreeNode.props(0, true))

    testNode ! Insert(testActor, id = 1, 42)
    expectMsg(OperationFinished(1))
    testNode ! Contains(testActor, id = 2, 42)
    expectMsg(ContainsResult(2, true))
  }


  test("simple inserts and lookups") {
    val topNode = system.actorOf(Props[BinaryTreeSet])

    topNode ! Contains(testActor, id = 1, 1)
    expectMsg(ContainsResult(1, false))

    topNode ! Insert(testActor, id = 2, 1)
    topNode ! Contains(testActor, id = 3, 1)

    expectMsg(OperationFinished(2))
    expectMsg(ContainsResult(3, true))
  }

  test("proper inserts and lookups") {
    val topNode = system.actorOf(Props[BinaryTreeSet])

    topNode ! Contains(testActor, id = 1, 1)
    expectMsg(ContainsResult(1, false))

    topNode ! Insert(testActor, id = 2, 1)
    topNode ! Contains(testActor, id = 3, 1)

    expectMsg(OperationFinished(2))
    expectMsg(ContainsResult(3, true))
  }