How do I mock DbSet.Add() for Entity Framework Core?

Question

I'm mocking a DbContext to auto-test classes that update the database.

I'm using Entity Framework Core and .NET 5.

Mock<MyDbContext> fakeDbContext = new Mock<MyDbContext>();

List<Book> availableBooks = new List<Book>(); // filled elsewhere

fakeDbContext.Setup(ct => ct.BookRepository).ReturnsDbSet(availableBooks);

This works fine, up to

fakeDbContext.BookRepository.Add(newBook);

The data from newBook show neither in BookRepository not in availableBooks.

So I guess I have to mock Add() further (I thought Setup().ReturnsDbSet() handled that, mistakenly it appears).

That would be the easiest way to call availableBooks.Add(). However, it has to return an EntityEntry<Book> object, which I haven't yet found how to create (it has a constructor, but not recommended for regular use).

I can't find any documentation on the matter, however. What can I try next?

Are using this by any chance: github.com/MichalJankowskii/Moq.EntityFrameworkCore ? — Fildor
– Fildor, Commented Jul 24 at 12:43
I looked into their examples and found that you probably need to do something like this: dotnetfiddle.net/W1YFC3 — Fildor
– Fildor, Commented Jul 24 at 13:18
^^ And that's because you are supposed to assume the DB operation was successful (you are NOT testing EFCore nor the Database, your "Unit" is the thing that is using the DbSet). — Fildor
– Fildor, Commented Jul 24 at 13:23
I just looked into some legacy code of ours and we were using MockQueryable, when we used to use Moq. I remember that there were some tests that were similar to yours. If I remember correctly, there may still be some setting up to do, though. — Fildor
– Fildor, Commented Jul 24 at 13:45
@Fildor: indeed, the "Moq.EntityFrameworkCore vs MockQueryable" section in this article I started out with states almost plainly that I should use MockQueryable for DB operations. I'm going to give it a try. — Jean-David Lanz
– Jean-David Lanz, Commented Jul 24 at 13:52

Jean-David Lanz · Accepted Answer · 2025-07-25 12:56:20Z

2

It being understood that the right answer is this one, I also want the question to get a straight answer, if nothing else because a few people upvoted it.

As mentioned in the comments, I tried Moq.EntityFrameworkCore and failed.

I succeeded with MockQueryable:

Mock<MyDbContext> fakeDbContext = new Mock<MyDbContext>();

List<Book> availableBooks = new List<Book>(); // filled elsewhere

Mock<DbSet<Book>> fakeBookRepository = availableBooks.AsQueryable().BuildMockDbSet();
fakeBookRepository.Setup(rp => rp.Add(It.IsAny<Book>()))
                  .Callback((Book bk) => availableBooks.Add(bk));
PseudoContexteMAS.Setup(ct => ct.DepotLivraison)
                 .Returns(fakeBookRepository.Object);

There ya go.

edited Jul 25 at 12:56

answered Jul 25 at 10:44

Jean-David Lanz

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DarkBee · Accepted Answer · 2025-07-25 10:52:20Z

0

First, Steve Py* is more than very likely right: what I'm doing here amounts to testing my repository. Which I should have no business doing.

So, well, that's the main answer here.

The point of a using a Repository is to provide a boundary for testing business logic around EF. The repository itself should not require unit testing. The end to end behaviour from data through to the application should be covered by integration tests that talk to a real database instance with known test data state. Have the repository return IQueryable then mock the repository to return the MockQueryable built mock.

edited Jul 25 at 10:52

DarkBee

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answered Jul 25 at 10:34

Jean-David Lanz

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