lukaszb/django-guardian — comment on commit cafd0a586756f1d463d1bcc463935db655ba0b45
File: guardian/tests/admin_test.py line 331
By funkaoshi:

This doesn't remove 'grappelli' from the installed applications list. (At least in our environment.) A more straightforward solution would seem to be to just restore the INSTALLED_APPS field:

settings.INSTALLED_APPS = org_settings.INSTALLED_APPS

You could avoid doing the copy at all and just cache that list when the class is built.