Mike Lively has posted about functionality he's created to add database testing procedures to preexisting PHPUnit tests supplementing his other post n adding database support to PHPUnit.

When I was first creating the Database Extension for PHPUnit I realized that there was a very high likelihood that several people would have tests that were already written that they would like to add additional database tests too. To accomplish this I actually wrote the PHPUnit_Extensions_Database_DefaultTester class. In fact, if you were to look at the source of the database test case you will see that all of it's operations are actually forwarded to this class which does all of the work.

He includes his same example from before - the banking system - and shows how the tests can be appended on, adding a getDatabaseTester method that returns an object the rest of the tests can use.