public void whenMoreThan2NumbersAreUsedThenExceptionIsThrown()
 {
     Assert.Throws(typeof(ArgumentException), () => StringCalculator2.Add("1,2,3"));
 }
 public void whenNonNumberIsUsedThenExceptionIsThrown()
 {
     Assert.Throws(typeof(FormatException), () => StringCalculator2.Add("1,x"));
 }
 public void whenEmptyStringIsUsedThenReturnValueIs0()
 {
     Assert.AreEqual(0, StringCalculator2.Add(""));
 }
 public void when2NumbersAreUsedThenNoExceptionIsThrown()
 {
     Assert.DoesNotThrow(() => StringCalculator2.Add("1,2"));
 }