using System.Collections.Generic; 
using System.Data.Entity; 
 
namespace TestingDemo 
{ 
    public class BloggingContext : DbContext 
    { 
        public virtual DbSet<Blog> Blogs { get; set; } 
        public virtual DbSet<Post> Posts { get; set; } 
    } 
 
    public class Blog 
    { 
        public int BlogId { get; set; } 
        public string Name { get; set; } 
        public string Url { get; set; } 
 
        public virtual List<Post> Posts { get; set; } 
    } 
 
    public class Post 
    { 
        public int PostId { get; set; } 
        public string Title { get; set; } 
        public string Content { get; set; } 
 
        public int BlogId { get; set; } 
        public virtual Blog Blog { get; set; } 
    } 
}

Virtual DbSet properties with the EF Designer

Note that the DbSet properties on the context are marked as virtual. This will allow the mocking framework to derive from our context and overriding these properties with a mocked implementation.

If you are using Code First then you can edit your classes directly. If you are using the EF Designer then you’ll need to edit the T4 template that generates your context. Open up the <model_name>.Context.tt file that is nested under you edmx file, find the following fragment of code and add in the virtual keyword as shown.

public string DbSet(EntitySet entitySet) 
{ 
    return string.Format( 
        CultureInfo.InvariantCulture, 
        "{0} virtual DbSet<{1}> {2} {{ get; set; }}", 
        Accessibility.ForReadOnlyProperty(entitySet), 
        _typeMapper.GetTypeName(entitySet.ElementType), 
        _code.Escape(entitySet)); 
}

Service to be tested

To demonstrate testing with in-memory test doubles we are going to be writing a couple of tests for a BlogService. The service is capable of creating new blogs (AddBlog) and returning all Blogs ordered by name (GetAllBlogs). In addition to GetAllBlogs, we’ve also provided a method that will asynchronously get all blogs ordered by name (GetAllBlogsAsync).

using System.Collections.Generic; 
using System.Data.Entity; 
using System.Linq; 
using System.Threading.Tasks; 
 
namespace TestingDemo 
{ 
    public class BlogService 
    { 
        private BloggingContext _context; 
 
        public BlogService(BloggingContext context) 
        { 
            _context = context; 
        } 
 
        public Blog AddBlog(string name, string url) 
        { 
            var blog = _context.Blogs.Add(new Blog { Name = name, Url = url }); 
            _context.SaveChanges(); 
 
            return blog; 
        } 
 
        public List<Blog> GetAllBlogs() 
        { 
            var query = from b in _context.Blogs 
                        orderby b.Name 
                        select b; 
 
            return query.ToList(); 
        } 
 
        public async Task<List<Blog>> GetAllBlogsAsync() 
        { 
            var query = from b in _context.Blogs 
                        orderby b.Name 
                        select b; 
 
            return await query.ToListAsync(); 
        } 
    } 
}

Testing non-query scenarios

That’s all we need to do to start testing non-query methods. The following test uses Moq to create a context. It then creates a DbSet<Blog> and wires it up to be returned from the context’s Blogs property. Next, the context is used to create a new BlogService which is then used to create a new blog – using the AddBlog method. Finally, the test verifies that the service added a new Blog and called SaveChanges on the context.

using Microsoft.VisualStudio.TestTools.UnitTesting; 
using Moq; 
using System.Data.Entity; 
 
namespace TestingDemo 
{ 
    [TestClass] 
    public class NonQueryTests 
    { 
        [TestMethod] 
        public void CreateBlog_saves_a_blog_via_context() 
        { 
            var mockSet = new Mock<DbSet<Blog>>(); 
 
            var mockContext = new Mock<BloggingContext>(); 
            mockContext.Setup(m => m.Blogs).Returns(mockSet.Object); 
 
            var service = new BlogService(mockContext.Object); 
            service.AddBlog("ADO.NET Blog", "http://blogs.msdn.com/adonet"); 
 
            mockSet.Verify(m => m.Add(It.IsAny<Blog>()), Times.Once()); 
            mockContext.Verify(m => m.SaveChanges(), Times.Once()); 
        } 
    } 
}

Testing query scenarios

In order to be able to execute queries against our DbSet test double we need to setup an implementation of IQueryable. The first step is to create some in-memory data – we’re using a List<Blog>. Next, we create a context and DBSet<Blog> then wire up the IQueryable implementation for the DbSet – they’re just delegating to the LINQ to Objects provider that works with List<T>.

We can then create a BlogService based on our test doubles and ensure that the data we get back from GetAllBlogs is ordered by name.

using Microsoft.VisualStudio.TestTools.UnitTesting; 
using Moq; 
using System.Collections.Generic; 
using System.Data.Entity; 
using System.Linq; 
 
namespace TestingDemo 
{ 
    [TestClass] 
    public class QueryTests 
    { 
        [TestMethod] 
        public void GetAllBlogs_orders_by_name() 
        { 
            var data = new List<Blog> 
            { 
                new Blog { Name = "BBB" }, 
                new Blog { Name = "ZZZ" }, 
                new Blog { Name = "AAA" }, 
            }.AsQueryable(); 
 
            var mockSet = new Mock<DbSet<Blog>>(); 
            mockSet.As<IQueryable<Blog>>().Setup(m => m.Provider).Returns(data.Provider); 
            mockSet.As<IQueryable<Blog>>().Setup(m => m.Expression).Returns(data.Expression); 
            mockSet.As<IQueryable<Blog>>().Setup(m => m.ElementType).Returns(data.ElementType); 
            mockSet.As<IQueryable<Blog>>().Setup(m => m.GetEnumerator()).Returns(data.GetEnumerator()); 
 
            var mockContext = new Mock<BloggingContext>(); 
            mockContext.Setup(c => c.Blogs).Returns(mockSet.Object); 
 
            var service = new BlogService(mockContext.Object); 
            var blogs = service.GetAllBlogs(); 
 
            Assert.AreEqual(3, blogs.Count); 
            Assert.AreEqual("AAA", blogs[0].Name); 
            Assert.AreEqual("BBB", blogs[1].Name); 
            Assert.AreEqual("ZZZ", blogs[2].Name); 
        } 
    } 
}

Testing with async queries

In order to use asynchronous queries we need to do a little more work. If we tried to use our Moq DbSet with the GetAllBlogsAsync method we would get the following exception:

System.InvalidOperationException: The source IQueryable doesn't implement IDbAsyncEnumerable<TestingDemo.Blog>. Only sources that implement IDbAsyncEnumerable can be used for Entity Framework asynchronous operations. For more details see http://go.microsoft.com/fwlink/?LinkId=287068.

In order to use the async methods we need to create an in-memory DbAsyncQueryProvider to process the async query. Whilst it would be possible to setup a query provider using Moq, it is much easier to create a test double implementation in code. The code for this implementation is as follows:

using System.Collections.Generic; 
using System.Data.Entity.Infrastructure; 
using System.Linq; 
using System.Linq.Expressions; 
using System.Threading; 
using System.Threading.Tasks; 
 
namespace TestingDemo 
{ 
    internal class TestDbAsyncQueryProvider<TEntity> : IDbAsyncQueryProvider 
    { 
        private readonly IQueryProvider _inner; 
 
        internal TestDbAsyncQueryProvider(IQueryProvider inner) 
        { 
            _inner = inner; 
        } 
 
        public IQueryable CreateQuery(Expression expression) 
        { 
            return new TestDbAsyncEnumerable<TEntity>(expression); 
        } 
 
        public IQueryable<TElement> CreateQuery<TElement>(Expression expression) 
        { 
            return new TestDbAsyncEnumerable<TElement>(expression); 
        } 
 
        public object Execute(Expression expression) 
        { 
            return _inner.Execute(expression); 
        } 
 
        public TResult Execute<TResult>(Expression expression) 
        { 
            return _inner.Execute<TResult>(expression); 
        } 
 
        public Task<object> ExecuteAsync(Expression expression, CancellationToken cancellationToken) 
        { 
            return Task.FromResult(Execute(expression)); 
        } 
 
        public Task<TResult> ExecuteAsync<TResult>(Expression expression, CancellationToken cancellationToken) 
        { 
            return Task.FromResult(Execute<TResult>(expression)); 
        } 
    } 
 
    internal class TestDbAsyncEnumerable<T> : EnumerableQuery<T>, IDbAsyncEnumerable<T>, IQueryable<T> 
    { 
        public TestDbAsyncEnumerable(IEnumerable<T> enumerable) 
            : base(enumerable) 
        { } 
 
        public TestDbAsyncEnumerable(Expression expression) 
            : base(expression) 
        { } 
 
        public IDbAsyncEnumerator<T> GetAsyncEnumerator() 
        { 
            return new TestDbAsyncEnumerator<T>(this.AsEnumerable().GetEnumerator()); 
        } 
 
        IDbAsyncEnumerator IDbAsyncEnumerable.GetAsyncEnumerator() 
        { 
            return GetAsyncEnumerator(); 
        } 
 
        IQueryProvider IQueryable.Provider 
        { 
            get { return new TestDbAsyncQueryProvider<T>(this); } 
        } 
    } 
 
    internal class TestDbAsyncEnumerator<T> : IDbAsyncEnumerator<T> 
    { 
        private readonly IEnumerator<T> _inner; 
 
        public TestDbAsyncEnumerator(IEnumerator<T> inner) 
        { 
            _inner = inner; 
        } 
 
        public void Dispose() 
        { 
            _inner.Dispose(); 
        } 
 
        public Task<bool> MoveNextAsync(CancellationToken cancellationToken) 
        { 
            return Task.FromResult(_inner.MoveNext()); 
        } 
 
        public T Current 
        { 
            get { return _inner.Current; } 
        } 
 
        object IDbAsyncEnumerator.Current 
        { 
            get { return Current; } 
        } 
    } 
}