public void ConstructorTest()
        {
            IStack <int> stack = new ResizingArrayStack <int>();

            Assert.IsTrue(stack.IsEmpty());
            Assert.AreEqual(0, stack.Size());
            Assert.IsTrue(string.IsNullOrWhiteSpace(stack.ToString()));
        }
        public void ToStringTest()
        {
            IStack <int> stack = new ResizingArrayStack <int>();

            for (int i = 0; i < 10; i++)
            {
                stack.Push(i);
            }
            Assert.AreEqual("9 8 7 6 5 4 3 2 1 0", stack.ToString());
        }