public void PostOrder_Test()
{
//arrange
BinarySearchTree myTree = new BinarySearchTree();
myTree.add(10);
myTree.add(5);
myTree.add(4);
myTree.add(13);
int[] expected = new int[] { 4, 5, 13, 10 };
//act
int[] actual = myTree.DepthHandler("postorder");
//Assert
Assert.Equal(expected, actual);
}