private static void ValidateInput(int size, BinaryTreeNode <int> expectedResult)
        {
            var result = Question4_2.MakeMinimalBinarySearchTree(Enumerable.Range(0, size).ToArray());

            TreeHelpers.AssertBinaryTreesAreEqual(result, expectedResult);
        }
 public void InvalidInputTest()
 {
     TestHelpers.AssertExceptionThrown(() => Question4_2.MakeMinimalBinarySearchTree(null), typeof(ArgumentNullException));
 }