Update to Django 1.8 – AttributeError: django.test.TestCase has no attribute ‘cls_atomics’

I believe the reason is that your setUpClass(cls) class method is not calling super. Because of that, django.tests.TestCase.setUpClass is not called and

cls.cls_atomics = cls._enter_atomics()

is not called, naturally causing cls_atomics to be undefined.

You should add super(ATestTests, cls).setUpClass() to your setUpClass.