Black Box Testing, Service Boundaries and Persistence

When testing persistence, I often write an NUnit test that programmatically creates a new entity, jams some data into (hard coded into my test) then calls a data access layer to persist it, then I create a new entity and ask my DAL to load it from the database (the same identifier I used to create it). Then I just compare the entities.

A developer I work with today showed me what he does. He creates an XML file with some test data and has a generic utitlity class to persist that into the database. He then creates a new entity