Defer server side imports in functional tests

[daviddavis]

The package signing tests imported AptPackageSigningService at module scope, which requires django.setup() to have run. That only happened as a side effect of the pytest-django plugin, which is declared in unittest_requirements.txt, so collection failed for anyone installing only functest_requirements.txt.

Route the signature check through a session fixture depending on django.setup(), which is how pulpcore initializes Django for functional tests. Adding pytest-django to functest_requirements.txt would also work, but it drags database fixtures into an HTTP only suite and makes Django mandatory for every functional test run.

Assisted-by: GitHub Copilot

[quba42]

Note: Adding pulp_rpm to my oci-env had the side effect of fixing my local test runs.

[daviddavis]

In pulp_rpm there's a pytest entry point here that loads the constants file and in that constants file, they are calling django.setup().

[daviddavis]

A couple alternatives to this change: call django.setup() at the top of the functional conftest (which is what pulp_rpm does), giving us a one-line fix that keeps the natural module-scope import, at the cost of making Django setup mandatory for every functional test run rather than just the signing tests. Or I could drop the server-side import entirely and reimplement the signature check in the functional test utils using python-gnupg, which is already in functest_requirements — that's roughly 30 lines of duplicated logic, but it removes the Django dependency from these tests completely and avoids the circularity of verifying the server's signing with the server's own verifier.