Database fixtures are run when they shouldn't be for SimpleTestCase unit tests

pytest-django uses a function internally for checking if a test is a Django test case class, named is_django_unittest. This class is used to determine if database setup is needed or not. This is implemented with an issubclass check for SimpleTestCase. However, the Django documentation states the following:

SimpleTestCase disallows database queries by default. This helps to avoid executing write queries which will affect other tests since each SimpleTestCase test isn’t run in a transaction.

See here: https://docs.djangoproject.com/en/1.10/topics/testing/tools/#django.test.SimpleTestCase.allow_database_queries

If you write a unit test in a TestCase class which inherits SimpleTestCase, where allow_database_queries is set to False, which is the default, you will hit problems when you have a fixture defined like so in your conftest.py file:

@pytest.fixture(autouse=True)
def setup_db_tenant(db):
    # ... Create something in the database here ...

The fixture will be run, and database access will be done, and then Django will print the following error message: (Where YourClassNameHere is whatever your class name is for your test case.)

AssertionError: Database queries aren't allowed in SimpleTestCase. Either use TestCase
or TransactionTestCase to ensure proper test isolation or set 
YourClassNameHere.allow_database_queries to True to silence this failure.

Start by tracing the is_django_unittest check and the database setup path described in the issue. Reproduce the autouse fixture with a SimpleTestCase whose allow_database_queries remains false, then verify that database fixtures are not run and the test no longer raises Django's database-query assertion.