Make unit tests cleanup a DB after finish

Unit tests don't cleanup a DB after successful finish.
It is an issue if I use one DB for all kind of tests. Especially with hardcoded primary keys in fixtures.

This fix make tests do a housekeeping after them.
I've just checked. It isn't called always. For me It wasn't called in case of exception in a test case or in a testable class.

So I think it is reasonable to keep it.