In odoo version 12 this test, worked fine:

def test_pep_category_after_economy_with_pep_is_created(self):
    partner = self.env["res.partner"].create({"name": "Sven Svan"})
    self.env["hemma_partner.partner_economy"].create({"partner_id": partner.id, "pep": PepSelection.PEP})
    pep_category = self.env.ref("hemma_partner.hemma_partner_category_pep")
    self.assertIsNotNone(pep_category)
    self.assertIn(pep_category.id, partner.category_id.ids)

Since we upgraded to odoo 14 it throws this error:

Traceback (most recent call last):2128 File "/home/odoo/odoo/odoo/addons/hemma_partner/tests/test_res_partner.py", line 43, in test_pep_category_after_economy_with_pep_is_created2129 self.assertIn(pep_category.id, partner.category_id.ids)2130 AssertionError: 3 not found in []2131

It seems like partner.category_id.ids are empty, is the behaviour of fetching category_id's changed in odoo 14?