+1. Looks like an improvement to me.
The calls to rollback() in the test cases are not actually needed, because (a) auto-commit is enabled, (b) BaseJDBCTestCase.tearDown() already calls rollback(), and (c) all the tests are read-only.
(The test originally had auto-commit disabled because setUp() called setAutoCommit(false). Calling setAutoCommit(false) from the decorator does not have the same effect because it uses a different Connection instance. This is just an observation, and I'm not suggesting that we should disable auto-commit again.)