public void PeekOrDefault()
        {
            Stack <int> stack = new Stack <int>();

            Assert.AreEqual(0, StackUtility.PeekOrDefault(stack));
            stack.Push(3);
            Assert.AreEqual(3, StackUtility.PeekOrDefault(stack));
            stack.Pop();
            Assert.AreEqual(0, StackUtility.PeekOrDefault(stack));
        }
        public void PeekOrDefaultWithDefault()
        {
            var stack = new Stack <int>();

            Assert.AreEqual(1, StackUtility.PeekOrDefault(stack, 1));
            stack.Push(3);
            Assert.AreEqual(3, StackUtility.PeekOrDefault(stack, 1));
            stack.Pop();
            Assert.AreEqual(1, StackUtility.PeekOrDefault(stack, 1));
        }