Mocking vs. Test DB?

Question

Earlier I asked this question How to correctly unit test my DAL?, one thing left unanswered for me is if to really test my DAL is to have a Test DB, then what is the role of

Answer 1

I didn't find mocking very useful when testing data access code. The purpose of unit testing is to verify the database-related code works and mocking the database would hinder the test.

Mocking does indeed become useful when testing the business code. You can mock your database calls to return test data and verify the behavior of business logic in those circumstances.

Regarding the use of transactions - it's certainly possible, as long as your architecture has room for starting a transaction at the beginning of the test, and then doing all database-related calls of your unit test inside that transaction. Never tried it, though.