An implementation of IDbSet to help with mocking Entity Framework DbContexts.

FakeDbSet.cs

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

namespace EntityExtensions {
    public class FakeDbSet<T> : System.Data.Entity.IDbSet<T> where T : class {
        private readonly List<T> list = new List<T>();

        public FakeDbSet() {
            list = new List<T>();
        }

        public FakeDbSet(IEnumerable<T> contents) {
            this.list = contents.ToList();
        }

        #region IDbSet<T> Members

        public T Add(T entity) {
            this.list.Add(entity);
            return entity;
        }

        public T Attach(T entity) {
            this.list.Add(entity);
            return entity;
        }

        public TDerivedEntity Create<TDerivedEntity>() where TDerivedEntity : class, T {
            throw new NotImplementedException();
        }

        public T Create() {
            throw new NotImplementedException();
        }

        public T Find(params object[] keyValues) {
            throw new NotImplementedException();
        }

        public System.Collections.ObjectModel.ObservableCollection<T> Local {
            get {
                throw new NotImplementedException();
            }
        }

        public T Remove(T entity) {
            this.list.Remove(entity);
            return entity;
        }

        #endregion

        #region IEnumerable<T> Members

        public IEnumerator<T> GetEnumerator() {
            return this.list.GetEnumerator();
        }

        #endregion

        #region IEnumerable Members

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
            return this.list.GetEnumerator();
        }

        #endregion

        #region IQueryable Members

        public Type ElementType {
            get { return this.list.AsQueryable().ElementType; }
        }

        public System.Linq.Expressions.Expression Expression {
            get { return this.list.AsQueryable().Expression; }
        }

        public IQueryProvider Provider {
            get { return this.list.AsQueryable().Provider; }
        }

        #endregion
    }
}

Very good. Thanks.