How do you mock your repositories?

Question

I've use Moq to mock my repositories. However, someone recently said that they prefer to create hard-coded test implementations of their repository interfaces.

What are the pros and cons of each approach?

Edit: clarified meaning of repository with link to Fowler.

Answer 1

I generally see two scenarios with repositories. I ask for something, and I get it, or I ask for something, and it isn't there.

If you are mocking your repository, that means you system under test (SUT) is something that is using your repository. So you generally want to test that your SUT behaves correctly when it is given an object from the repository. And you also want to test that it handles the situation properly when you expect to get something back and don't, or aren't sure if you are going to get something back.

Hard-coded test doubles are ok if you are doing integration testing. Say, you want to save an object, and then get it back. But this is testing the interaction of two objects together, not just the behavior of the SUT. They are two different things. If you start coding fake repositories, you need unit tests for those as well, otherwise you end up basing the success and failure of your code on untested code.

That's my opinion on Mocking vs. Test Doubles.