Creating an IEnumerable<int> from a string

IEnumerableRangeTest.cs

//Thanks to BLUEPIXY for adding -number handling and overall a better implementation
    [TestFixture]
    public class IEnumerableRangeTest {
        static public IEnumerable<int> GetRange(int start, int end){
            int step = (start > end)? -1:1;
            for (int i = start; true ; i += step){
                yield return i;
                if(i == end) break;
            }
        }
    
        static public IEnumerable<int> GetRange(string numbers) {
            var items = numbers.Split(',');
            var rangeRegex = new Regex(@"(-?\d+)-(-?\d+)");
            foreach(var item in items) {
                if(!string.IsNullOrWhiteSpace(item)) {
                    int result;
                    if(int.TryParse(item, out result)) {
                        yield return result;
                        continue;
                    } else if(rangeRegex.IsMatch(item)) {
                        var m = rangeRegex.Match(item);
                        foreach (var n in GetRange(int.Parse(m.Groups[1].Value), int.Parse(m.Groups[2].Value))){
                            yield return n;
                        }
                        continue;
                    }
                    throw new InvalidCastException(string.Format("Unable to cast \"{0}\" to an int", item));
                }
            }
        }



        [Test]
        public void range_of_comma_separated_values_results_in_ten_elements() {
            string range = "0,1,2,3,4,5,6,7,8,9";
            var result = GetRange(range).ToList();

            Assert.AreEqual(0, result.First());
            Assert.AreEqual(9, result.Last());
            Assert.AreEqual(10, result.Count());
        }

        [Test]
        public void range_of_mixed_values_results_in_20_elements() {
            string range = "0,1,2,3,4,5,6,7,8,9,10-19";
            var result = GetRange(range).ToList();

            Assert.AreEqual(0, result.First());
            Assert.AreEqual(19, result.Last());
            Assert.AreEqual(20, result.Count());
        }

        [Test]
        public void range_of_1_to_9_contains_9_elements() {
            string ranges = "1-9";

            var result = GetRange(ranges).ToList();
            Assert.AreEqual(1, result.First());
            Assert.AreEqual(9, result.Last());
            Assert.AreEqual(9, result.Count());
        }

        [Test]
        public void individual_number_contains_one_element() {
            string number = "1";

            var result = GetRange(number).ToList();
            Assert.AreEqual(1, result.First());
            Assert.AreEqual(1, result.Count());
        }

        [Test, ExpectedException(typeof(InvalidCastException))]
        public void invalid_number_throws_InvalidCastException() {
            string range_with_invalid_number = "invalid";

            GetRange(range_with_invalid_number).ToList();
        }
    }