Tennis game kata in C# from http://codingdojo.org/cgi-bin/wiki.pl?KataTennis

DefineTennisGame.cs

using NUnit.Framework;

namespace TennisScoringKata
{
    [TestFixture]
    public class DefineTennisGame
    {
        private TennisGame game;

        [SetUp]
        public void Setup()
        {
            game = new TennisGame("Thing 1", "Thing 2");
        }

        [Test]
        public void ReturnsLoveLoveForANewGame()
        {
            Assert.That(game.Score, Is.EqualTo("love-love"));
        }

        [Test]
        public void Returns15LoveWhenTheServerScoresOnce()
        {
            game.Volley("Thing 1");
            Assert.That(game.Score, Is.EqualTo("15-love"));
        }

        [Test]
        public void Returns30LoveWhenTheServerScoresTwice()
        {
            game.Volley("Thing 1");
            game.Volley("Thing 1");
            Assert.That(game.Score, Is.EqualTo("30-love"));
        }

        [Test]
        public void Returns40LoveWhenTheServerScoresThreeTimes()
        {
            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");
            Assert.That(game.Score, Is.EqualTo("40-love"));
        }

        [Test]
        public void ReturnGameWhenTheServerScoresFourTimes()
        {
            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");
            Assert.That(game.Score, Is.EqualTo("game Thing 1"));
        }

        [Test]
        public void ReturnsLove15WhenTheNonServerScoresOnce()
        {
            game.Volley("Thing 2");
            Assert.That(game.Score, Is.EqualTo("love-15"));
        }

        [Test]
        public void ReturnsLove30WhenTheNonServerScoresTwice()
        {
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            Assert.That(game.Score, Is.EqualTo("love-30"));
        }

        [Test]
        public void ReturnsLove40WhenTheNonServerScoresThreeTimes()
        {
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            Assert.That(game.Score, Is.EqualTo("love-40"));
        }

        [Test]
        public void ReturnsGameWhenTheNonServerScoresFourTimes()
        {
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            Assert.That(game.Score, Is.EqualTo("game Thing 2"));
        }

        [Test]
        public void ReturnsDeuceWhenBothPlayersScoreThreeTimes()
        {
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");

            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");

            Assert.That(game.Score, Is.EqualTo("deuce"));
        }

        [Test]
        public void ReturnsDeuceWhenBothPlayersScoreFourTimes()
        {
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");

            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");

            Assert.That(game.Score, Is.EqualTo("deuce"));
        }

        [Test]
        public void ReturnsAdvantageServerWhenServerScoresAfterDeuce()
        {
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");

            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");

            Assert.That(game.Score, Is.EqualTo("advantage Thing 1"));
        }

        [Test]
        public void ReturnsAdvantageNonServerWhenNonServerScoresAfterDeuce()
        {
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");

            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");

            game.Volley("Thing 2");

            Assert.That(game.Score, Is.EqualTo("advantage Thing 2"));
        }

        [Test]
        public void ReturnsGameWhenServerScoresTwiceAfterDeuce()
        {
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");

            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");

            game.Volley("Thing 1");
            game.Volley("Thing 1");

            Assert.That(game.Score, Is.EqualTo("game Thing 1"));
        }

        [Test]
        public void ReturnsGameWhenNonServerScoresTwiceAfterDeuce()
        {
            game.Volley("Thing 2");
            game.Volley("Thing 2");
            game.Volley("Thing 2");

            game.Volley("Thing 1");
            game.Volley("Thing 1");
            game.Volley("Thing 1");

            game.Volley("Thing 2");
            game.Volley("Thing 2");

            Assert.That(game.Score, Is.EqualTo("game Thing 2"));
        }
    }
}

TennisGame.cs

using System;

namespace TennisScoringKata
{
    class TennisGame
    {
        private int[] points = new int[2];
        private string server;
        private string nonServer;

        public TennisGame(string server, string nonServer)
        {
            this.server = server;
            this.nonServer = nonServer;
        }

        public string Score
        {
            get
            {
                if (points[0] >= 3 && points[1] >= 3 && Math.Abs(points[0] - points[1]) < 2)
                    if (points[0] == points[1])
                        return "deuce";
                    else if (points[0] > points[1])
                        return "advantage " + server;
                    else
                        return "advantage " + nonServer;
                
                if (points[0] < 4 && points[1] < 4)
                    return TranslateScore(points[0]) + "-" + TranslateScore(points[1]);
                
                if (points[0] >= 4)
                    return TranslateScore(points[0]) + " " + server;

                return TranslateScore(points[1]) + " " + nonServer;
            }
        }

        internal void Volley(string scoringPlayer)
        {
            if (scoringPlayer == server)
                points[0]++;
            else
                points[1]++;
        }

        static string TranslateScore(int points)
        {
            switch (points)
            {
                case 3:
                    return "40";
                case 2:
                    return "30";
                case 1:
                    return "15";
                case 0:
                    return "love";
                default:
                    return "game";
            }
        }
    }
}