C# CodeKata (Bowlling Game Kata)

Game.cs

using System.Collections.Generic;
using System.Linq;

namespace BowllingGamaKata
{
    public class Game
    {
        private List<int> rolls;

        public Game()
        {
            this.rolls = new List<int>();
        }

        public void Roll(int pins)
        {
            this.rolls.Add(pins);
        }

        public int Score()
        {
            var currentIndex = 0;

            var totalScore = Enumerable.Range(1, 10).
                Select(_ =>
                {
                    if (IsStrike(currentIndex))
                    {
                        var strikeScore = 10 + StrikeBonus(currentIndex);
                        currentIndex++;
                        return strikeScore;
                    }

                    if (IsSpare(currentIndex))
                    {
                        var spareScore = 10 + SpareBonus(currentIndex);
                        currentIndex += 2;
                        return spareScore;
                    }

                    var noBonusScore = SumOfPinsInFrame(currentIndex);
                    currentIndex += 2;
                    return noBonusScore;
                }).
                Sum();

            return totalScore;
        }

        private int SumOfPinsInFrame(int currentIndex)
        {
            return this.rolls.ElementAt(currentIndex) 
                    + this.rolls.ElementAt(currentIndex + 1);
        }

        private int SpareBonus(int currentIndex)
        {
            return this.rolls.ElementAt(currentIndex + 2);
        }

        private int StrikeBonus(int currentIndex)
        {
            return this.rolls.ElementAt(currentIndex + 1)
                    + this.rolls.ElementAt(currentIndex + 2);
        }

        private bool IsStrike(int currentIndex)
        {
            return this.rolls.ElementAt(currentIndex) == 10;
        }

        private bool IsSpare(int currentIndex)
        {
            return this.rolls.ElementAt(currentIndex)
                    + this.rolls.ElementAt(currentIndex + 1) == 10;
        }
    }
}

GameTest.cs

using System.Linq;
using NUnit.Framework;
using BowllingGamaKata;

namespace BowllingGamaKataTest
{
    [TestFixture]
    public class GameTest
    {
        private Game g;

        [SetUp]
        public void SetUp()
        {
            this.g = new Game();
        }

        [Test]
        public void パーフェクトゲーム()
        {
            foreach (var i in Enumerable.Range(0, 12))
            {
                RollStrike();
            }

            Assert.AreEqual(300, this.g.Score());
        }

        [Test]
        public void ストライクを１回とる()
        {
            RollStrike();
            g.Roll(4);
            g.Roll(5);
            RollMany(0, 16);
            Assert.AreEqual(28, g.Score());
        }

        private void RollStrike()
        {
            g.Roll(10);
        }

        [Test]
        public void スペアを１回とる()
        {
            RollSpare();
            g.Roll(3);
            RollMany(0, 17);
            Assert.AreEqual(16, g.Score());
        }

        private void RollSpare()
        {
            g.Roll(5);
            g.Roll(5);
        }

        [Test]
        public void 全フレームガター()
        {
            RollMany(0, 20);
            Assert.AreEqual(0, g.Score());
        }

        [Test]
        public void 全投球で１本ずつ倒す()
        {
            RollMany(1, 20);
            Assert.AreEqual(20, g.Score());
        }

        private void RollMany(int pins, int count)
        {
            foreach (var i in Enumerable.Range(0, count))
            {
                g.Roll(pins);
            }
        }
    }
}