[3dprinter-general] Bug#1118139: slic3r-prusa: flaky autopkgtest 'check-gui' on at least riscv64

[Simon McVittie]

Source: slic3r-prusa
Version: 2.9.3+dfsg-2
Severity: important
User: debian-riscv at lists.debian.org
Usertags: riscv64
Justification: https://release.debian.org/testing/rc_policy.txt §6a
User: debian-ci at lists.debian.org
Usertags: flaky
Control: affects -1 + src:glib2.0

The 'check-gui' autopkgtest for slic3r-prusa intermittently fails on 
ci.debian.net on riscv64:

https://ci.debian.net/packages/s/slic3r-prusa/testing/riscv64/

The testing migration infrastructure assumes this is a regression in a 
package that was upgraded, preventing packages like glib2.0 from 
migrating to testing until the slic3r-prusa autopkgtest is retried. This 
bug report is likely to be escalated to RC if it becomes a practical 
problem for migrations.

If this test is expected to be unreliable, it could be marked with 
"Restrictions: flaky" so that it isn't used to gate migrations from 
unstable to testing:

    Tests: check-gui
    Depends: ...
    Restrictions: allow-stderr, flaky, needs-root

Or it could be marked with the "skippable" restriction:

    Tests: check-gui
    Depends: ...
    Restrictions: allow-stderr, needs-root, skippable

and do its own logic to classify its results into three buckets, using 
an exit status convention borrowed from Autotools:

* success: exit 0
* skipped, expected/ignorable failure or other neutral status: exit 77
* failure: any other exit status

This test runs as root, uses su to drop privileges, starts a window 
manager and the app, waits for an arbitrary 30 seconds and takes 
screenshots. This seems sufficiently high-complexity that it is going to 
be difficult to make it 100% reliable, especially on slow machines like 
riscv64 where 30 seconds might not be enough.

Some suggestions that might make it more reliable, or at least easier to 
see what has gone wrong by silencing irrelevant warnings:

* Instead of using needs-root to do setup as root and then dropping
  privileges, it would be more realistic if you either used needs-sudo
  and used 'sudo localedef ...' to ensure that the en_US.UTF-8 locale
  was present, or added a dependency on locales-all. In particular this
  would avoid having a wrong XDG_RUNTIME_DIR set.

* In fact you don't need to be root at all: you can generate locales
  in a temporary directory without privileges, and set LOCPATH
  (see debian/tests/run-with-locales in the glib2.0 source package).

* You can suppress warning messages about AT-SPI by running with
  NO_AT_BRIDGE=1 (GTK 3 or older) and/or GTK_A11Y=none (GTK 4).

* The warning "Could not load a pixbuf from..." can be fixed by adding
  a dependency on librsvg2-common, which contains the SVG loader for
  gdk-pixbuf.

Thanks,
    smcv