public void Delete4_123_Returns123()
{
SingleLinkedList <int> list = new SingleLinkedList <int>();
list.InsertAtEnd(1);
list.InsertAtEnd(2);
list.InsertAtEnd(3);
list.Delete(4);
int[] numbers = list.ToArray();
Assert.AreEqual(new int[] { 1, 2, 3 }, numbers);
}