code: def fail(self) -> None:
          
  
          _debug("fail")
  
          # on commit carry out action; on rollback reverse rename
          def on_commit(_obj):
              raise_testfailure("commit")
  
          def on_rollback(_obj):
              raise_testfailure("rollback")
  
          return self._process(on_commit, on_rollback)
docs: for testing purposes only. always fail in commit