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

By using a test database, you open up the possibility that problems could be caused at the database itself or along the communication path (network, etc) between the DAL and database. Mocking eliminates those possibilities.