modify_settings decorator append operation failing

[Mark Rogaski]

I am using autodiscover_modules in a project to load app URL configurations. After moving from 1.10.6 to 1.11.1, the test app that I was using for unit testing is failing.

In the project urls.py:

from django.utils.module_loading import autodiscover_modules

from myproject import site

autodiscover_modules('urls', register_to=site)

In the unit test:

from django.test import TestCase, modify_settings

@modify_settings(INSTALLED_APPS={
    'append': 'myproject.tests.testapp'
})
class UrlRegistryTest(TestCase):
    ...

When stepping through with the debugger, I see that INSTALLED_APPS isn't modified when the autodiscover function is called in 1.11.

[Tim Graham]

Could you ​bisect to find the commit where the behavior changed?

[Mark Rogaski]

Replying to Tim Graham:

Could you ​bisect to find the commit where the behavior changed?

I'll start looking. Thanks.

[Tim Graham]

Please reopen if you provide further details. I couldn't reproduce an issue given the minimal details in the ticket.