public void Roman_Valid_99(string roman, string romanDigitsCommaSeprated)
        {
            IEnumerable <string> letterParser = new RomanLetterParser(roman);

            var romanDigits = romanDigitsCommaSeprated.Split(',');

            int index = 0;

            foreach (var letter in letterParser)
            {
                Assert.AreEqual(romanDigits[index++], letter);
            }
        }
        public void Roman_InValid_990(string roman, string romanDigitsCommaSeprated)
        {
            IEnumerable <string> letterParser = new RomanLetterParser(roman);

            var romanDigits = romanDigitsCommaSeprated.Split(',');

            int index = 0;

            Assert.Throws <ArgumentException>(() =>
            {
                foreach (var letter in letterParser)
                {
                    Assert.AreEqual(romanDigits[index++], letter);
                }
            });
        }