public void Sub_SubstractingWhereStackCountIsLessThanTwo_ThrowsException()
{
var calc = new StackCalculator();
calc.Push(100);
Exception e = Assert.Throws<ArgumentException>(() => calc.Sub());
}
public void Sub_SubstractingValues_ValuesSubstracted()
{
var calc = new StackCalculator();
calc.Push(100);
calc.Push(200);
calc.Sub();
Expect(calc.Pop(), Is.EqualTo(200-100));
}