In the end, I used a straight forward implementation of the strategy pattern and everything worked out. And this second time around, I started with an integration test, got that working and worked my way from there.

It was a good learning opportunity though.

In our zest to fine tune unit testing (mocks and all) , we often forget that there is only so much that unit testing can achieve.

Where I work, most of the work is highly database intensive. Database and its wrappers (ORM tools etc.) introduce their own level of complexity and we try to test them as early as possible in the development cycle.