Thursday, May 3, 2018

I continued to work on #2296.

I tried to reproduce it on my machine by installing exactly the same environment as on travis (using the output of their “pip freeze” as requirement in a virgin environment. Nope! The problem remains unreproducible!

But then I stumbled over the Order in which tests are executed section of the Django docs.

IOW: while Django differentiates three groups of test cases, and while the test methods of a single TestCase class are ordered alphabetically, no such ordering rule is defined for the files themselves. They are run with no particular ordering guaranteed nor enforced among them. It might therefore be possible that the order is always a particular one (but always the same) on my machine and always another on the travis machine.

And here is a first partly success: indeed I can reproduce the problem on my machine by the –reverse <https://docs.djangoproject.com/en/1.11/ref/django-admin/#cmdoption-test-reverse>` option:

$ dm test --reverse

My explanation for the problem: my testcase_setup <lino.core.signals.testcase_setup> signal (which is used to call clear_site_config is being emitted by lino.utils.djangotest.DjangoManageTestCase.__call__() but that’s too late. Django loads the fixtures before calling the test method.

By looking into the code of django.test.testcases I saw that it emits a signal django.test.signals.setting_changed before loading the fixtures.

So the solution for #2296 is to simply connect lino.modlib.system.my_handler() (which calls clear_site_config) to Django’s setting_changed signal as well.

Side effect: I removed the lino.core.signals.database_connected signal as it is never used.

Wow! This ticket has been haunting me for several months, with a few occasional attempts to fix it (each time just to discover that it is a tough one), and now it took me about two working days of intensive bug hunting to find it!