I see what you are saying, but no matter what integration tests like your example are tricky to write. But keep in mind that while you do feed the results into DBD::Mock, there is nothing to prevent you from feeding in incorrect results, or results you know will mess things up. In fact, that is one of the things it is best at, simulating error conditions that would otherwise require you to make a mess out of your database.
In alot of cases, I like to develop against a real database, because in the end, that is the situation it needs to work in. It just makes sense to me to do it this way. After I am satisfied my module works, I have been converting the live DB test code to use DBD::Mock and adding tests at the end to also verify my SQL statements. The conversion from DBD::mysql to DBD::Mock is pretty minimal, it only requires that a seed my results, which is much easier than writing the code to make, manage and destroy test database.
