def METHOD_NAME(self):
    zaak = ZaakFactory.create()
    zaak_url = f"http://testserver{reverse(zaak)}"
    BesluitFactory.create(zaak=zaak)
    response = self.client.delete(zaak_url)
    self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
    error = get_validation_errors(response, "nonFieldErrors")
    self.assertEqual(error["code"], "related-besluiten")