FizzBuzzerTests.cs

    [TestFixture]
    public class FizzBuzzerTests
    {
        [Test]
        public void OneHundredElementsSeparatedByCommas()
        {
            Assert.AreEqual(100, SplitFizzBuzzString().Length);
        }

        [Test]
        public void NumbersDivisibleByThreeStartWithFizz([Range(3, 99, 3)] int number)
        {
            Assert.IsTrue(GetFizzBuzzElement(number).StartsWith("Fizz"));
        }

        [Test]
        public void NumbersDivisibleByFiveEndWithBuzz([Range(5, 100, 5)] int number)
        {
            Assert.IsTrue(GetFizzBuzzElement(number).EndsWith("Buzz"));
        }

        [Test]
        public void RemainingNumbersAreUnchanged([ValueSource("unchangedNumbers")] int number)
        {
           Assert.AreEqual((number).ToString(), GetFizzBuzzElement(number));
        }

        private IEnumerable<int> unchangedNumbers()
        {
            return Enumerable.Range(1, 100).Where(n => n%3 != 0 && n%5 != 0);
        }

        private string GetFizzBuzzElement(int number)
        {
            return SplitFizzBuzzString()[number - 1];
        }

        private string[] SplitFizzBuzzString()
        {
            return new FizzBuzzer().FizzBuzz().Split(',');
        }
    }

    public class FizzBuzzer
    {
        public string FizzBuzz()
        {
            string[] sequence = new string[100];
            for (int index = 2; index < 99; index += 3)
            {
                sequence[index] = "Fizz";
            }
            for (int index = 4; index < 100; index += 5)
            {
                sequence[index] += "Buzz";
            }
            for (int index = 0; index < 100; index++)
            {
                if (sequence[index] == null)
                {
                    sequence[index] = (index + 1).ToString();
                }
            }
            return String.Join(",", sequence);
        }
    }