Django DB records disappears after first testcase run

I'm working on a project based on Django REST Framework. So I need to write some test cases for my REST API.

I've written some basic class (let's call it BaseAPITestCase) inherited from standard DRFs APITransactionTestCase.

In this class I've defined setUp method where I'm creating some test user which belongs to some groups (I'm using UserFactory written with FactoryBoy).

When I run my tests, the first one (first test case method from first child class) successfully creates a user with specified groups, but the others don't (other test case methods in the same class).

User groups just don't exist in DB at this time. It seems like existed records are deleted from DB at each new test case run. But how then it works for the first time?

I've read Django test documentation but can't figure out why it happens... Can anyone explain it?

The main question is what I should do to make these tests works?

Should I create user once and store it in object variable?

Should I add some params to preserve user groups data?

Or should I add user groups to fixtures? In that case, how can I create this fixture properly? (All related models, such as permissions and content types)

Simplified source code for illustration:

from rest_framework.test import APITransactionTestCase    

class BaseAPITestCase(APITransactionTestCase):

    def setUp(self):
        self.user = UserFactory(
            username='login',
            password='pass',
            group_names=('admin', )
        )
        self.client = APIClient()
        self.client.force_login(self.user)

    def tearDown(self):
        self.client.logout()    

class CampaignListTest(BaseAPITestCase):

    def test_authorized_get(self):
        # successfully gets user groups from DB

    def test_authorized_post(self):
        # couldn't find any groups