It's the job of the DB package to perform as specified. The problem is that one can write code that works correctly under the wrong assumptions of DB behavior.

It's the job of the DB package to perform as specified. The problem is that one can write code that works correctly under the wrong assumptions of DB behavior. Here's an example I've experienced: We were building (to be purposefully vague) an auction system where an auction could end at any point in time. Bids flowed in via a queue. It didn't really matter within reason which order the bids were processed, but we had to make sure that a bid which caused an auction to end was processed in isolation from other bids that depended on the auction still being open. Our code relied upon the DB's locking behaviors (SELECT FOR UPDATE) to ensure that the code processing a particular bid laid claim to the state (auction status, etc) used for its work. All fine and good except that we didn't quite understand how Oracle implemented locking at various isolation levels. So, some code which would have worked against, say, DBUnit, failed under Oracle. This wasn't a failure of the DB, but we wouldn't have caught this problem unless we ran an integration test.