public void TestSecondTop()
{
IFancyCalculator x = new FancyCalculator();
x.Push(25);
x.Push(10);
x.Push(15);
Assert.IsTrue(x.SecondTop() == 10);
}
public void TestSecondTopFailureToRespond()
{
IFancyCalculator x = new FancyCalculator();
Assert.IsNull(x.SecondTop());
}