Django doesn't create test database when running test

Question

I read in Django document that a blank database will be created for testing. I am new to Django so I barely changed anything in setting.py and currently using Sqlite database. However, when I run python manage.py test, Django keep telling the user has been existed, so I tried changing the username for the created users in TestCase, run the test again and found out that the new users are created in the existing database. The test file is as bellow:

class UserTestCase(unittest.TestCase):
    def setUp(self):
        admin = User.objects.create(username="admin", password="1")
        user1 = User.objects.create(username="user1", password="1")
        user2 = User.objects.create(username="user2", password="1")
        admin.following.add(user1)
        admin.followers.add(user2)

    def test_users_count(self):
        self.assertEqual(User.objects.count()==3)

My model is as bellow:

class User(AbstractUser):
    followers = models.ManyToManyField('self', related_name="following", symmetrical=False, through='Follow', through_fields=('followee', 'follower'))
    
    def __str__(self):
        return f"{self.username}"

    def serialize(self):
        return {
            "id": self.id,
            "username": self.username,
        }

class Follow(models.Model):
    followee = models.ForeignKey(
        'User',
        on_delete=models.CASCADE,
        related_name='+'
    )
    follower = models.ForeignKey(
        'User',
        on_delete=models.CASCADE,
        related_name='+'
    )

    def clean(self, *args, **kwargs):
        if self.follower__id == self.followee__id:
            raise ValidationError('Can not follow self.')
        return super().clean(*args, **kwargs)
    
    class Meta:
        constraints = [
            models.UniqueConstraint(fields=['follower', 'followee'], name='follow_once'),
            models.CheckConstraint(check=~Q(follower=F('followee')), name='not_follow_self')
        ]

EDIT: Bellow is the output when I run python manage.py test

(env_web) PS C:\Users\HL94NVT\Programming\web_development\project4> python manage.py test
System check identified no issues (0 silenced).
EE
======================================================================
ERROR: test_following_count (network.tests.UserTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 84, in _execute       
    return self.cursor.execute(sql, params)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\sqlite3\base.py", line 413, in execute
    return Database.Cursor.execute(self, query, params)
sqlite3.IntegrityError: UNIQUE constraint failed: network_user.username

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Users\HL94NVT\Programming\web_development\project4\network\tests.py", line 21, in setUp
    admin = User.objects.create(username="admin1", password="1")
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\query.py", line 447, in create
    obj.save(force_insert=True, using=self.db)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\contrib\auth\base_user.py", line 67, in save
    super().save(*args, **kwargs)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\base.py", line 754, in save
    force_update=force_update, update_fields=update_fields)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\base.py", line 792, in save_base
    force_update, using, update_fields,
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\base.py", line 895, in _save_table
    results = self._do_insert(cls._base_manager, using, fields, returning_fields, raw)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\base.py", line 935, in _do_insert
    using=using, raw=raw,
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\query.py", line 1254, in _insert
    return query.get_compiler(using=using).execute_sql(returning_fields)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\sql\compiler.py", line 1397, in execute_sql
    cursor.execute(sql, params)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 66, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 75, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\sqlite3\base.py", line 413, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.IntegrityError: UNIQUE constraint failed: network_user.username

======================================================================
ERROR: test_users_count (network.tests.UserTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\sqlite3\base.py", line 413, in execute
    return Database.Cursor.execute(self, query, params)
sqlite3.IntegrityError: UNIQUE constraint failed: network_user.username

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Users\HL94NVT\Programming\web_development\project4\network\tests.py", line 21, in setUp
    admin = User.objects.create(username="admin1", password="1")
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\query.py", line 447, in create
    obj.save(force_insert=True, using=self.db)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\contrib\auth\base_user.py", line 67, in save
    super().save(*args, **kwargs)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\base.py", line 754, in save
    force_update=force_update, update_fields=update_fields)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\base.py", line 792, in save_base
    force_update, using, update_fields,
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\base.py", line 895, in _save_table
    results = self._do_insert(cls._base_manager, using, fields, returning_fields, raw)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\base.py", line 935, in _do_insert
    using=using, raw=raw,
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\query.py", line 1254, in _insert
    return query.get_compiler(using=using).execute_sql(returning_fields)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\models\sql\compiler.py", line 1397, in execute_sql
    cursor.execute(sql, params)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 66, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 75, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "C:\Users\HL94NVT\Programming\web_development\env_web\lib\site-packages\django\db\backends\sqlite3\base.py", line 413, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.IntegrityError: UNIQUE constraint failed: network_user.username

----------------------------------------------------------------------
Ran 2 tests in 0.063s

Answer 1

Using django.test.TestCase instead of unittest.TestCase helps according to the document https://docs.djangoproject.com/en/3.1/topics/testing/overview/

If your tests rely on database access such as creating or querying models, be sure to create your test classes as subclasses of django.test.TestCase rather than unittest.TestCase.

Using unittest.TestCase avoids the cost of running each test in a transaction and flushing the database, but if your tests interact with the database their behavior will vary based on the order that the test runner executes them. This can lead to unit tests that pass when run in isolation but fail when run in a suite.