Broken monkey-patching in humanize tests

[Aymeric Augustin]

The tests for django.contrib.humanize monkey-patch the datetime module in django.utils.timesince as follows:

        timesince.datetime = new.module(b"mock_datetime")
        timesince.datetime.datetime = MockDateTime

Unfortunately, this means that isinstance(d, datetime.datetime) in django.utils.timesince will return False while the monkey-patch is in effect even though d is a real datetime.datetime.

The humanize tests rely on a fixed value: now = datetime.datetime(2012, 3, 9) which happens to be at 0h00. They pass by accident, really. Add an hour and a minute to now — this shouldn't matter at all — and they'll fail!

This is preventing me from writing correct tests for #18504, because datetime objects are treated as date objects and their time part is ignored. It's impossible to write tests for edge cases around DST changes with this bug.

I hope I don't need to explain how horrible this was to debug :(

[Aymeric Augustin]

This patch restricts the monkey-patching to the module that is currently tested, namely humanize. This isn't perfect but it's less insane.

I'll review the patch (at first sight, we should also remove orig_timesince_datetime) and push it.

[Aymeric Augustin <aymeric.augustin@…>]

In [123362dd37a076987f265179fe16dcd2b6a16d12]:

Fixed #18608 -- Reduced monkey-patching in tests.

Thanks Claude Paroz for the patch.