I have been using NHibernate for a while now and am happy writing test cases / mocks for Repository implementations such that my code never need hit a database. I have also used Entity Framework in the past and have a soft spot for it, and recently came across a post by the Entity Framework team saying that EF v6 is actually very testable and we can/could use it directly in our codebase.
Naturally I wanted to try this out, so I tried it out using EF6 using Repositories and directly and was pleasantly surprised with the results which I have documented in this article:
Hope that helps someone out. Enjoy