The frame class

Frame.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
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 virtual int Total { get { return FirstThrow + SecondThrow; } }

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

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

        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;
        }
    }
}