MemoryDbSet for DbContext Unit Testing

MemoryDbSet.cs

using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Linq.Expressions;

namespace Barkeep.Tests
{
    public class MemoryDbSet<T> : DbSet<T>, IQueryable<T> where T : class
    {
        #region Private Members

        private readonly HashSet<T> _set;

        #endregion

        #region Constructors

        public MemoryDbSet() : this(Enumerable.Empty<T>())
        {
        }

        public MemoryDbSet(IEnumerable<T> entities)
        {
            _set = new HashSet<T>();
            foreach (var entity in entities)
            {
                _set.Add(entity);
            }
            var queryable = _set.AsQueryable();
            Provider = queryable.Provider;
            Expression = queryable.Expression;
        }

        #endregion

        #region Public Methods

        public override T Add(T entity)
        {
            _set.Add(entity);
            return entity;
        }

        public override T Remove(T entity)
        {
            _set.Remove(entity);
            return entity;
        }

        public override T Find(params object[] keyValues)
        {
            var id = -1;
            if (keyValues.Count() == 1)
            {
                id = keyValues.First() is int ? (int) keyValues.First() : -1;
            }
            return _set.SingleOrDefault(x =>
                (x.GetType().GetProperty("ID", typeof (int)).GetValue(x) is int
                    ? (int) x.GetType().GetProperty("ID", typeof (int)).GetValue(x)
                    : 0) == id);
        }

        public override IEnumerable<T> RemoveRange(IEnumerable<T> entities)
        {
            _set.RemoveWhere(entities.Contains);
            return _set;
        }

        public IEnumerator<T> GetEnumerator()
        {
            return _set.AsQueryable().GetEnumerator();
        }

        public IQueryProvider Provider { get; private set; }

        public Expression Expression { get; private set; }

        #endregion
    }

    #region Extensions

    public static class Extensions
    {
        public static DbSet<T> ToMockDbSet<T>(this IEnumerable<T> list) where T : class
        {
            return new MemoryDbSet<T>(list);
        }
    }

    #endregion
}