pytest fixture for SQLAlchemy tests to wrap each test in its own transaction, which is automatically rolled back when the test completes. Drop into a test module to enable for each test in that module. Or, put it into a package's conftest.py to enable it for every test in that package.

conftest.py

@pytest.fixture(autouse=True)
def close_transaction(request):
	session.begin(subtransactions=True)
	request.addfinalizer(session.rollback)