EF4 - possible to mock ObjectContext for unit testing?

Question

Can it be done without using TypeMock Islolator? I've found a few suggestions online such as passing in a metadata only connection string, however nothing I've come across besides TypeMock seems to truly allow for a mock ObjectContext that can be injected into services for unit testing. Do I plunk down the $$ for TypeMock, or are there alternatives? Has nobody managed to create anything comparable to TypeMock that is open source?

Answer 1

I'm unit testing EF4 easily without mocking. What I did was create a repository interface using the code from http://elegantcode.com/2009/12/15/entity-framework-ef4-generic-repository-and-unit-of-work-prototype/ as a basis I then created an InMemoryRepository<T> class that used the IRepository interface. I then replaced the IObjectSet<T> with a List<T> inside of the class and changed the retrieval methods accordingly.

Thus if you need to do unit testing, pass in the InMemoryRepository rather than the DataRepository.

Answer 2

Put your Linq2Entity query behind an interface, unit test it in isolation against a real database.

Write tests for your business logic with mocks for your query interfaces. Don't let Linq bleed into your business logic!

Don't use the RepositoryPattern!