How to implement FakeObjectSet : IObjectSet, about EF 4 unit testing

Hello,

This is actually a great question! FakeObjectSet is not a class included in the framework but just a placeholder name for any fake implementation of the IObjectSet interface. I can share with you right now a very simple version that we often use to implement fake ObjectContext classes for unit tests:

using System;

using System.Collections;

using System.Collections.Generic;

using System.Data.Objects;

using System.Linq;

using System.Linq.Expressions;

using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace Testing

{

    class FakeObjectSet : IObjectSet where TEntity : class

    {

        HashSet _data;

        IQueryable _query;

        public FakeObjectSet() : this(new List()) { } 

        public FakeObjectSet(IEnumerable testData)

        {

            _data = new HashSet(testData);

            _query = _data.AsQueryable();

        }

        public void AddObject(TEntity item)

        {

            _data.Add(item);

        }

        public void DeleteObject(TEntity item)

        {

            _data.Remove(item);

        }

        public void Attach(TEntity item)

        {

            _data.Add(item);

        }

        IEnumerator IEnumerable.GetEnumerator()

        {

            return _data.GetEnumerator();

        }

        IEnumerator IEnumerable.GetEnumerator()

        {

            return _data.GetEnumerator();

        }

        Type IQueryable.ElementType

        {

            get { return _query.ElementType; }

        }

        Expression IQueryable.Expression

        {

            get { return _query.Expression; }

        }

        IQueryProvider IQueryable.Provider

        {

            get { return _query.Provider; }

        }

    }

}

You will find a brief sample on how to use this in the Sneak Peak blog post I wrote about Testability Improvements in EF 4, here.

Hope this helps