How to test code with regular database level errors?

Question

Django

When I register in a view, the following happens:

if form.is_valid():
        try:
            user = User.objects.create_user(
                email=form.cleaned_data['email'],
                password=form.cleaned_data['password1']
            )
        except IntegrityError:
            user = User.objects.get(email=form.cleaned_data['email'])
            ...

Everything works as it should. But can't test this code in django.test.TestCase:

ERROR: test_registration_when_existing_inactive_email (accounts.test_views.SignupTest)
---------------------------------------- ------------------------------
Traceback (most recent call last):
...
return self.cursor.execute(sql, params)
psycopg2.IntegrityError: ERROR: Duplicate key value violates unique constraint "accounts_user_email_key"
DETAIL: Key "(email)=([email protected])" already exists.
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
...
return self.cursor.execute(sql, params)
django.db.utils.IntegrityError: ERROR: Duplicate key value violates unique constraint 'accounts_user_email_key'
DETAIL: Key '(email)=([email protected])' already exists.
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
...
django.db.transaction.TransactionManagementError: An error occurred in the current transaction. You can't execute queries until the end of the 'atomic' block.
-------------------------------------------------- --------------------
Ran 16 tests in 1.498s
FAILED (errors=1)
Destroying test database for alias 'default'...

Obviously IntegrityError interferes with the test, but this error is normal behavior. How to test such code?