public void TestPop()
{
IRPNCalculator c = new RPNCalculator();
Assert.True(c.Size() == 0);
c.Push(6);
c.Push(5);
Assert.True(c.Size() == 2 && c.Top() == 5);
c.Pop();
Assert.True(c.Size() == 1 && c.Top() == 6);
}