Unit test to reproduce a problem with mongoengine inheritance. I need to save instances of child class in different collection, and have no idea how to do it.

inheritance_tests.py

from django.test import TestCase
import mongoengine as me

class TestCollectionNameInheritance(TestCase):
    def test_simple_case(self):
        class BasicUser(me.Document):
            username=me.StringField(required=True, unique=True)
            meta = {
                'allow_inheritance': True,
                # 'indexes': [
                #     {'fields': ['username'], 'unique': True}
                # ]
            }

        class CorporateUser(BasicUser):
            title = me.StringField(required=False)
            # meta = {
            #     'collection': 'corporate_user'
            # }


        CorporateUser._meta['collection'] = 'corporate_user'

        BasicUser.drop_collection()
        CorporateUser.drop_collection()

        customer_username = 'customer'
        basic = BasicUser(username=customer_username)
        basic.save()

        username='ceo_user'
        u = CorporateUser(username=username, title='CEO')
        u.save()

        self.assertEqual(BasicUser.objects._collection.name, 'basic_user')
        self.assertEqual(CorporateUser._meta['collection'], 'corporate_user')
        self.assertEqual(CorporateUser.objects._collection.name, 'corporate_user')

        self.assertEqual(CorporateUser.objects(username=username).count(), 1)
        self.assertEqual(BasicUser.objects(username=username).count(), 0)
        
        db = BasicUser._get_db()
        self.assertEqual(db['basic_user'].find({'username': username}).count(), 0)
        self.assertEqual(db['corporate_user'].find({'username': username}).count(), 1)

        self.assertEqual(db['basic_user'].find({'username': customer_username}).count(), 1)
        self.assertEqual(db['corporate_user'].find({'username': customer_username}).count(), 0)