How we can use H2 in Memory database to enhance JUNITS?

Our organization is slowly adapting to using Agile methodology and trying to adapt to the new processes and shorter time lines. We have always been laying a lot of stress on JUNITs which currently run after a successful build where we mock some of the objects.

I wanted to know if you can share your experiences and advise using in Memory Databases like H2 for JUNITs where we can create tables and data before the JUNITS run so that we work with close to real application data, table structures and functionality rather than mocking the DAOs. The database is later cleaned up at the end of the tests.