DB not flushed between TestCases

[Lokesh Gurram]

Consider the case where I have two fixtures and two different TestCase classes that use them.

fixture1.json

[
{
    "model": "app1.user",
    "pk": 1,
    "fields": {
        "password": "",
        "last_login": null,
        "is_superuser": false,
        "username": "tesuser1",
        "first_name": "",
        "last_name": "",
        "is_staff": false,
        "is_active": true,
        "date_joined": "2020-02-21T12:59:17.302Z",
        "email": null,
        "groups": [],
        "user_permissions": []
    }
}
]

fixture2.json

[
{
    "model": "app1.user",
    "pk": 2,
    "fields": {
        "password": "",
        "last_login": null,
        "is_superuser": false,
        "username": "testuser2",
        "first_name": "",
        "last_name": "",
        "is_staff": false,
        "is_active": true,
        "date_joined": "2020-02-21T12:59:17.302Z",
        "email": null,
        "groups": [],
        "user_permissions": []
    }
}
]

Here are my test cases

class Test1(TestCase):
    fixtures = ['fixture1.json']

    @classmethod
    def tearDownClass(cls):
        super(TestCase, cls).tearDownClass()

    def test_demo(self):
        u = User.objects.get(username='testuser1')
        #some testing

class Test2(TestCase):
    fixtures = ['fixture2.json']

    @classmethod
    def tearDownClass(cls):
        super(TestCase, cls).tearDownClass()

    def test_demo2(self):
        try:
            u = User.objects.get(username='testuser1')
            print("Found him")
            #Some testing
        except:
            pass

I wouldn't expect to find testuser1 in my second test case as the fixtures for it doesn't have that particular user.

From django documentation:
At the start of each test, before setUp() is run, Django will flush the database, returning the database to the state it was in directly after migrate was called.

[ChillarAnand]

What command are you using to run the tests? Is this happening with a new django project?

I created a new django project with the above fixtures and tests. It is working as expected?

# test1
test_demo (tests.test_user.Test1) ... <QuerySet [<User: tesuser1>]>

# test2
test_demo2 (tests.test_user.Test2) ... <QuerySet [<User: testuser2>]>

[Simon Charette]

You're explicitly calling super(TestCase, cls).tearDownClass() ​which skips fixtures teardown.

Please use TicketClosingReasons/UseSupportChannels for further assitance

[Lokesh Gurram]

If I have more than one TestCase using the same fixture, loading data between test cases raises unique constraint violation error

class Test1(TestCase):
    fixtures = ['fixture.json']

    def test_demo(self):
        u = User.objects.get(username='testuser1')
        #some testing

class Test2(TestCase):
    fixtures = ['fixture.json']

    def test_demo2(self):
        #some testing
        pass

where my fixture.json is
Profile table has a one-to-one relation with User table.

[
{
    "model": "app1.user",
    "pk": 1,
    "fields": {
        "password": "",
        "last_login": null,
        "is_superuser": false,
        "username": "testuser1",
        "first_name": "",
        "last_name": "",
        "is_staff": false,
        "is_active": true,
        "date_joined": "2020-02-21T12:59:17.302Z",
        "email": null,
        "groups": [],
        "user_permissions": []
    }
},
{
    "model": "app1.profile",
    "pk": 1,
    "fields": {
        "user": 1,
        "firebaseID": null,
        "phone": null,
        "completed_till": 0,
    }
}
]

Running the each Test Case separately works fine. But when run them in one go, first Test case goes through and before second test case executes, I get this error -

django.db.utils.IntegrityError: Problem installing fixture 'C:\...\app1\fixtures\fixture.json': Could not load app1.Profile(pk=1): duplicate key value violates unique constraint "app1_profile_user_id_key"

Making an explicit call to tearDownClass helped in fixing this issue but it gave the problem I first posted here.

Any idea why the DB is not completely cleared before trying to load the fixtures for the next TestCase. I tested this with Django 2.2 on Postgres 10/12. The problem persists in both.
Interestingly though testing on SQLite doesn't give any problem.