public void Given_empty_array_When_convert_Then_return_null()
 {
     Assert.AreEqual(null, ConvertSortedArrayToBinarySearchTree.SortedArrayToBST(new int[] { }));
 }
        public void Given_array_2_item_When_convert_Then_return_root()
        {
            var result = ConvertSortedArrayToBinarySearchTree.SortedArrayToBST(new int[] { 1, 2 });

            Assert.AreEqual(1, result.val);
        }