How to mock ObjectContext or ObjectQuery in Entity Framework?

Question

How to mock ObjectContext or ObjectQuery in Entity Framework?

Answer 1

I agree with the others you cannot really Mock ObjectContext. You should use EF DbContext because you can mock the underlying DbSet There are quite a lot of post how to do that. So I won't write how to do it. However if you absolutely must use ObjectContext (for some reason) and you want to Unit test it you can use InMemory database.

First install this Nuget package: Effort (Entity Framework Fake ObjectContext Realization Tool), which uses NMemory as the database. Install Effort.EF6 package:

PM> Install-Package Effort.EF6

using System;
using System.Data.Common;
using System.Data.Entity;
using System.Data.Entity.Core.Objects;
using System.Data.Entity.Infrastructure;
using Effort;

public class DbContextHelper
{
    //Fake object you can drop this if you are using your own EF context
    private class DbObject
    {
        public Guid Id { get; set; }
        public string Name { get; set; }
    }

    //Fake EF context you can switch with you own EF context
    private class FakeDbContext : DbContext
    {
        public FakeDbContext(DbConnection connection)
            : base(connection, true) { }

        public virtual DbSet DbObjects { get; set; }
    }

    private FakeDbContext _dbContext;

    public DbContextHelper()
    {
        //In memory DB connection
        DbConnection effortConnection = DbConnectionFactory.CreatePersistent("TestInstanceName");
        _dbContext = new FakeDbContext(effortConnection);
    }

    //You can expose your context instead of the DbContext base type
    public DbContext DbContext => _dbContext;

    public ObjectContext ObjectContext => ((IObjectContextAdapter)_dbContext).ObjectContext;

    //Method to add Fake object to the fake EF context
    public void AddEntityWithState(string value, EntityState entityState)
    {
        DbContext.Entry(new DbObject() { Id = Guid.NewGuid(), Name = value }).State = entityState;
    }
}

Usage:

DbContextHelper _dbContextHelper = new DbContextHelper();
_dbContextHelper.AddEntityWithState("added", System.Data.Entity.EntityState.Added);
_dbContextHelper.AddEntityWithState("added", System.Data.Entity.EntityState.Modified);

var objs = _dbContextHelper.ObjectContext.GetObjectStateEntries(EntityState.Modified | EntityState.Added);

There you are you have your object in memory DB.