bug#57691: 29.0.50; image-tests failures

[Eli Zaretskii]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Fri, 9 Sep 2022 18:37:20 -0400
> Cc: 57691@debbugs.gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > What does that test check? why does it want to see the delay?
> 
> It used to just check that no metadata was returned for these images.
> Then Lars changed the GIF and WebP loading code to always add a `delay',
> so I adapted the tests to that.

Is it important to verify that the 'delay' stuff is in metadata?  If
not, how about just removing that part of the test?

> > The native APIs support animated GIFs better than with libgif, so
> > artificially making changes of the delay for the single benefit of
> > running this test is not the best idea, IMO.
> 
> Gotcha.  So it sounds like we should leave that alone, and adapt the
> test to Windows instead.
> 
> Does the below workaround make sense?  That way, at least we test
> something.

I'd rather we skipped the test if w32-use-native-image-API is non-nil.
That's because my expectations are that once Emacs 29 hits the street,
people will stop building Emacs on Windows with libgif (and a few
other image libraries which the native APIs can replace), so setting
the variable to nil will probably mean you'd need to check
image-type-available-p again etc.  That sounds like an unnecessary
complication.

And once again, perhaps that part of the test should simply be
removed, as I don't see why we'd need to verify the metadata.

Thanks.