Mocking DbContext with fluent API configuration

Question

In Entity Framework you can configure the relationship between your entities by either using data annotations inside the actual class entity:

public class Entity
{
    [Key, Column(Order = 0)]
    public Guid PartOfPrimaryKey { get; set; }

    [Key, Column(Order = 1)]
    public Guid AlsoPartOfPrimaryKey { get; set; }
}

or by using the fluent API configuration

    modelBuilder.Entity<Entity>()
                .HasKey(k => new { k.PartOfPrimaryKey, k.AlsoPartOfPrimaryKey });

Give that you've used the fluent API configruation approach, how do you make sure the configuration is executed while mocking (using Moq) the DbContext for unit testing?

When i mock the DbContext the method OnModelCreating is not being executed.

Here is an explanation of how to test your application using a mocking framwork, but it doesn't explain how they take care of the problem with "configuring" the entities. Other posts I have found doesn't address this issue either. I guess there's something simple i'm missing.

Sidenote: I'm also aware of that it might not be a good idea at all to unit test your DbContext because you will use LINQ to Objects in your tests and LINQ to entites in production. However, I still think there is an answer to my question.

Update: If I use the data annotations instead, it works fine.

Answer 1

I'd never mock an ORM. I prefer to create intermediate classes that implement an interface (for example a repository) and mock that interface. However, let's see what I can do for you:

A good way to mock a DbContext for unit testing that will work with Fluent API, annotations, and so on, is to use an in-memory DB. Even if it's a DB is still fast enough for unit testing. It also allows you to mock an insert-read or insert-update-read sequence in a transparent way.

Please, see this Q&A (and don't take the accepted answer as the best one, because it isn't):

Is there an in-memory provider for Entity Framework?