public void Add_AddingValues_ValuesAdded()
 {
     var calc = new StackCalculator();
     calc.Push(100);
     calc.Push(200);
     calc.Add();
     Expect(calc.Pop(), Is.EqualTo(300));
 }
 public void Add_AddingWhereStackCountIsLessThanTwo_ThrowsException()
 {
     var calc = new StackCalculator();
     calc.Push(100);
     Exception e = Assert.Throws<ArgumentException> ( () => calc.Add() );
 }