BinaryTreeSuite.scala

  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))
  }