tests: end-to-end tests not working on macOS

[GraemeWatt]

With my current set-up (MacBook Pro with Apple M2 Pro chip running macOS Tahoe 26.0.1), running the end-to-end tests (pytest tests/e2e) gives Fatal Python error: Segmentation fault. The workarounds mentioned in #928 do not help. This might be due to:

hepdata/tests/e2e/conftest.py

Line 65 in 3b79786

multiprocessing.set_start_method('fork')

The Python docs say "The fork start method should be considered unsafe as it can lead to crashes of the subprocess as macOS system libraries may start threads. See bpo-33725."

I tried switching to the spawn start method or removing the use of multiprocessing altogether, but I got other errors. The end-to-end tests should be modified to avoid relying on the fork start method. I'll add some explanation to the installation docs in the meantime that the end-to-end tests might not work on macOS.

As an aside, I don't see that the line TEST_RUNNER="celery.contrib.test_runner.CeleryTestSuiteRunner", in both tests/conftest.py and tests/e2e/conftest.py is doing anything. This seems to be something from Django.

@ItIsJordan : maybe something for you to work on?

[GraemeWatt]

The CI is passing after the changes made in the Copilot PR #930, but after checking out the branch copilot/fix-e2e-tests-on-macos I still get errors locally. I've tried running the tests both using a Sauce Connect tunnel and running Selenium locally using ChromeDriver. Some tests are successful (e.g. pytest tests/e2e/test_general.py) but others give errors. For example, pytest tests/e2e/test_accounts.py gives:

FAILED tests/e2e/test_accounts.py::test_user_registration_and_login[Chrome] - AssertionError: Should not be authenticated
ERROR tests/e2e/test_accounts.py::test_user_registration_and_login[Chrome] - AssertionError: Errors in browser log:

@ItIsJordan : can you run the end-to-end tests locally on your laptop without errors? If you get the same errors, the problem is likely not specific to macOS.