bug#57150: 29.0.50; [PATCH] Add test coverage for overlay modification hooks

[Eli Zaretskii]

> From: Matt Armstrong <matt@rfc20.org>
> Cc: 57150@debbugs.gnu.org
> Date: Sat, 13 Aug 2022 21:52:22 -0700
> 
> Thanks Eli, another patch attached.  More comments below.

This is very good, thanks!

> Ironically, after all this was done, I am left wondering if a well
> designed macro fixture wouldn't be more clear, simply because it does
> produce a separate ERT test for each test case.  Perhaps there are ways
> to design macro test fixtures in clear ways to avoid the downsides of
> the way they appear in the other buffer-tests.el tests today....

It is okay to make several tests in a single ert-deftest test, as long
as each failing test is clearly explained and easily correlated to the
source code that failed.