I've recently been using JPA for the persistence layer of a project, and I'm liking it a lot. As I am a firm believer in TDD I've been applying this to the persistence layer of my application, and I thought that I'd share my approach to this.

The persistence layer uses Hibernate as the JPA provider and for test purposes this is great as it allows the RDBMS to be changed with relative ease.

In order to test the integration of the JPA provider with an RDBMS I will be using HSQLDB as the the RDBMS. This has the benefit of having a very lightweight in-memory execution model that makes it quick and easy to set up and tear down the entire database infrastructure. HSQLDB won't actually be the production RDBMS (this is likely to be MySQL), however the JPA/Hibernate combination makes it fairly trivial to use different RDBMS engines.