bug#59328: 29.0.50; `seq-keep' implementation only valid for lists

[Eli Zaretskii]

> From: Michael Heerdegen <michael_heerdegen@web.de>
> Cc: 59328@debbugs.gnu.org,  larsi@gnus.org,  jonas@bernoul.li
> Date: Thu, 24 Nov 2022 14:04:27 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > > #+begin_src emacs-lisp
> > > (defun seq-keep (function sequence)
> > >   (seq-filter #'identity (seq-map function sequence)))
> > > #+end_src
> >
> > This makes sense to me, so please go ahead and install, preferably
> > with a test for non-list cases.
> 
> I don't think adding a test case to Emacs is possible - all currently
> existing counterexamples I found (stream.el, myers.el) are in Elpa or
> somewhere else, but not in the Emacs repo.

I don't understand: why cannot we add a test to Emacs, even though other
tests are elsewhere?

> So I guess it's ok to go without a test?

It's okay, but I'd prefer to have a test.