public void SingleCharacterStringToInteger()
        {
            var input = new ConvertStringToInteger("9");

            Assert.Equal(9, input.GetIntegerValue());
        }
        public void StringContainingLetter()
        {
            var input = new ConvertStringToInteger("a897");

            Assert.Throws <ArgumentException>(() => input.GetIntegerValue());
        }
        public void NegativeStringToInteger()
        {
            var input = new ConvertStringToInteger("-5897");

            Assert.Equal(-5897, input.GetIntegerValue());
        }
        public void StringStartingWithZero()
        {
            var input = new ConvertStringToInteger("0897");

            Assert.Equal(897, input.GetIntegerValue());
        }
        public void TwoCharactersStringToInteger()
        {
            var input = new ConvertStringToInteger("97");

            Assert.Equal(97, input.GetIntegerValue());
        }