Typically the approach I take is monkey patch out the transaction methods (begin, commit, rollback) in the test harnesses and wrap each test in a real transaction. Some test runners have this built in.

This is easy in dynamic languages, really hard in in static languages.

You could use savepoints instead to wrap the transaction.

Not sure how Django handles exactly it but it works really well transparently. The only issue is when the code you are testing rolls back a nested transaction, I seem to remember that caused issues but there is a workaround at least

One approach we used was to wrap the connections in a proxy (easy in Python), and flag if the code called the commit() method at any point. You do need to trust that the code doesn't call COMMIT explicitly via the execute() method, and flag tests running subprocesses that might dirty the database. If the test is dirty, rebuild the test database from the template instead of relying on rolling back the transactions.

However, if you add this behavior to an existing test suite you will likely have to fix a lot of tests assuming sequences will return predictable numbers, such as in automatically generated primary keys. Technically, these tests are already broken even if it is unlikely to see them fail.

We make tests robust in the face of existing data. For example, each name is "GUID-ified", we only compare specific subsets of rows that we know will be isolated from the rest etc...

We still use transaction rollback for most of our tests, but all tests are written with the assumption of existing data, to accommodate for the few tests that must commit their transactions (such as concurrency tests).

Eh I have run hundreds of tests in Django in like 15 seconds