In-memory implementation of IDbSet, for unit testing.

MemoryDbSet.cs

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

public class MemoryDbSet<T> : IDbSet<T> where T : class {
    readonly List<T> _list = new List<T>();

    public MemoryDbSet() {
        _list = new List<T>();
    }

    public MemoryDbSet(IEnumerable<T> contents) {
        _list = contents.ToList();
    }

    public T Add(T entity) {
        _list.Add(entity);
        return entity;
    }

    public T Attach(T entity) {
        _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 ObservableCollection<T> Local {
        get {
            throw new NotImplementedException();
        }
    }

    public T Remove(T entity) {
        _list.Remove(entity);
        return entity;
    }

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

    IEnumerator IEnumerable.GetEnumerator() {
        return _list.GetEnumerator();
    }

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

    public Expression Expression {
        get { return _list.AsQueryable().Expression; }
    }

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