void InternalTest(int?[] tree, int expected)
        {
            TreeNode root   = TreeNode.Get(tree);
            int      actual = MaxDepthBinaryTree.MaxDepth(root);

            Assert.Equal <int>(expected, actual);
        }
        public void FindMaxBinaryTreeHeightTests(object[] treeNodes, int expectedHeight)
        {
            // arrange
            var root = TreeNode.Build(treeNodes);

            // act
            int height = MaxDepthBinaryTree.MaxDepth(root);

            // assert
            Assert.AreEqual(expectedHeight, height);
        }