Bowling Score Calculator Kata from Daedtech.com Alternative Design Question - http://www.daedtech.com/tdd-for-breaking-problems-apart-3-finishing-up

Frame.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.VisualStudio.TestTools.UnitTesting;
 
namespace ScratchPadTest
{
    public class Frame
    {
        public static Frame Strike { get { return new Frame(10, 0); } }

        public class UnderflowException : Exception { }

        public class OverflowException : Exception { }

        protected const int Mark = 10;

        public int FirstThrow { get; protected set; }

        public int SecondThrow { get; protected set; }

        public bool IsStrike { get { return FirstThrow == Frame.Mark; } }

        public bool IsSpare { get { return !IsStrike && BaseTotal == Frame.Mark; } }

        public virtual int Total(Frames previousFrames)
        {
            int total = BaseTotal;

            if (WereLastTwoFramesStrikes(previousFrames))
                total += BaseTotal + FirstThrow;
            else if (WasLastFrameAStrike(previousFrames))
                total += BaseTotal;
            else if (WasLastFrameASpare(previousFrames))
                total += FirstThrow;

            return total;
        }

        private int BaseTotal { get { return FirstThrow + SecondThrow; } }

        private bool WereLastTwoFramesStrikes(Frames frames)
        {
            return WasLastFrameAStrike(frames) && frames.Count > 1 && frames.BackFromLast(2).IsStrike;
        }

        private bool WasLastFrameAStrike(Frames frames)
        {
            return frames.Count > 0 && frames.Last.IsStrike;
        }

        private bool WasLastFrameASpare(Frames frames)
        {
            return frames.Count > 0 && frames.BackFromLast(1).IsSpare;
        }

        protected Frame() { }

        public Frame(int firstThrow, int secondThrow)
        {
            if (firstThrow < 0 || secondThrow < 0)
                throw new UnderflowException();
            if (firstThrow + secondThrow > Mark)
                throw new OverflowException();

            FirstThrow = firstThrow;
            SecondThrow = secondThrow;
        }
    }
}