How to mockup Entity Framework 6 With Moq & Autofixture

Question

I am using AutoMoq but I am kinda confused how to write my first unit test because of Entity Framework's (using EF6 and code first) dbContext

// in service class(constructor)
private readonly MyContext context;

public PriceService(MyContext context)
{
    this.context = context;
}

// following would be in nunit test method.
var fixture = new Fixture().Customize(new AutoMoqCustomization());
var priceService = fixture.Create<PriceService>();

When I run the unit test it crashes

    at Ploeh.AutoFixture.Kernel.TerminatingSpecimenBuilder.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.RecursionGuard.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.Postprocessor`1.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.RecursionGuard.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.Postprocessor`1.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.RecursionGuard.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.AutoPropertiesCommand`1.Execute(Object specimen, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.Postprocessor`1.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.RecursionGuard.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.Postprocessor`1.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.RecursionGuard.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.Postprocessor`1.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.RecursionGuard.Create(Object request, ISpecimenContext context)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
    at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.MethodInvoker.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.Postprocessor`1.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.RecursionGuard.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.Postprocessor`1.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.Kernel.CompositeSpecimenBuilder.c__DisplayClass6.b__1(ISpecimenBuilder b)
    at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
    at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
    at System.Linq.Enumerable.d__a5`1.MoveNext()
    at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
    at Ploeh.AutoFixture.Kernel.RecursionGuard.Create(Object request, ISpecimenContext context)
    at Ploeh.AutoFixture.SpecimenFactory.Create[T](ISpecimenContext context, T seed)
    at Ploeh.AutoFixture.SpecimenFactory.Create[T](ISpecimenContext context)
    at PriceServiceTests.Test_Price_Object_Setup() in PriceServiceTests.cs:line 26

Edit

In EF 6 seems like they are making the DbSet more mockable.

https://entityframework.codeplex.com/wikipage?title=Design%20Meeting%20Notes%20-%20May%2016%2c%202013

Make DbSet more mockable

• These means adding a protected constructor and making methods virtual
• Note that a type derived from DbSet that uses the protected constructor would create an object not be bound to any context and the methods would be no-ops. This makes it very like IDbSet from the perspective of creating test doubles.
• If we took this option we could potentially obsolete IDbSet
• It’s worth noting that no cases have been identified where this would be functionally different to using IDbSet for test doubles. However, there is strong feeling in the community that interfaces are preferred.

Anyone know how to mock it up?

Edit 2

I found this article but it keeps crashing

public class MyContext : DbContext
{
    //public GroceryListContext()
    //    : base()
    //{

    //}
    public virtual DbSet<Price> Prices { get; set; }
}

[Test]
public void Test_Price_Object_Setup_Properly()
{
    var mockContext = new Mock<MyContext>();

    var mockSet = new Mock<DbSet<Price>>(); // had to add EF to my test solution.
    mockContext.Setup(m => m.Prices).Returns(mockSet.Object);
    var service = new PriceService(mockContext.Object);

    // dies when using autofixture so thought try first moq like in article
   //var priceService = fixture.Create<PriceService>();

   Assert.That(true, Is.EqualTo(false));
}

with the following exception:

MyContext.Tests.Services.PriceServiceTests.Test_If_Price_Object_Setup_Properly: System.ArgumentException : Type to mock must be an interface or an abstract or non-sealed class. ----> System.TypeLoadException : Method 'Create' on type 'DbSet1Proxyb409fc6b430b4568aac048b60ea2f02e' from assembly 'DynamicProxyGenAssembly2, Version=0.0.0.0, Culture=neutral, PublicKeyToken=a621a9e7e5c32e69' tried to implicitly override a method with weaker type parameter constraints`.

Answer 1

You need to supply a specification which indicates that the DbSet<T> class should be mocked (although it's not an abstract type or interface).

The reason for that is because the DbSet<T> class is public but it has a protected constructor.

Specification:

internal class DbSetTypeSpecification : IRequestSpecification
{
    public bool IsSatisfiedBy(object request)
    {
        var type = request as Type;
        if (type == null)
            return false;

        return type.IsGenericType
            && typeof(DbSet<>) == type.GetGenericTypeDefinition();
    }
}

Example:

[Fact]
public void Test()
{
    var fixture = new Fixture();
    fixture.ResidueCollectors.Add(
        new MockRelay(
            new DbSetTypeSpecification()));

    Assert.DoesNotThrow(() => 
        fixture.Create<PriceService>());
}

Now AutoFixture can provide auto-generated PriceService values.

---

Please note that the MyContext class is also public and, AFAICT, it has a public constructor too. This means that AutoFixture will not supply an auto-mocked instance for MyContext class by default.

(If you can provide your scenario I might be able to help further.)

Answer 2

There is a NuGet Package called AutoFixture.AutoEF which may solve your issue

fixture.Customize(new EntityCustomization(new DbContextEntityTypesProvider(typeof(MyContext))));