private static void ValidateResult <T>(Node <T> input, params T[] expectedResult)
            where T : IEquatable <T>
        {
            var input1 = ListHelpers.CloneList(input);
            var input2 = ListHelpers.CloneList(input);

            Question2_1.RemoveDuplicates(input1);
            Question2_1.RemoveDuplicatesNoSpace(input2);

            ListHelpers.ValidateLinkedListContent(input1, expectedResult);
            ListHelpers.ValidateLinkedListContent(input2, expectedResult);
        }
 public void InvalidInputsTest()
 {
     // Null input string
     TestHelpers.AssertExceptionThrown(() => { Question2_1.RemoveDuplicates <int>(null); }, typeof(ArgumentNullException));
     TestHelpers.AssertExceptionThrown(() => { Question2_1.RemoveDuplicatesNoSpace <int>(null); }, typeof(ArgumentNullException));
 }