parent and child domain replication
The PeriodMixin extend the domain of the fields parent and childs in the __setup__. But as it is in the base class, this replace the definition of the base field (which is copied in Model.__setup__) and so the extension is recursively applied on each call to __setup__ by module. This fails running all the tests on all modules because __setup__ is called many time and so a very large domain is created overflowing the SQLite stack.