Get "NoneType" exception and fail to perform cold-boot and warm-boot stress test

[baconYao]

Bug Description

Problem

Unable to perform cold-boot-loop-reboot1 and warm-boot-loop-reboot1 since the TypeError: 'NoneType' object is not iterable exception be thrown.

This issue can be 100% reproduced by installing Checkbox22 Version: 2.9.0 (Rev: 473), but no this problem while using Checkbox22 Version: 2.8.0 (Rev: 437).

---------------------------[ Perform cold reboot 1 ]----------------------------
ID: com.canonical.certification::cold-boot-loop-reboot1
Category: com.canonical.certification::stress-tests/cold-boot
Waiting for the system to shut down or reboot...
Traceback (most recent call last):
  File "/snap/checkbox22/current/bin/checkbox-cli", line 8, in <module>
    sys.exit(main())
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/checkbox_cli.py", line 163, in main
    subcmd.invoked(ctx)
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/subcommands.py", line 261, in invoked
    self._run_jobs(self.ctx.sa.get_dynamic_todo_list())
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/stages.py", line 375, in _run_jobs
    builder = self._run_single_job_with_ui_loop(
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/stages.py", line 189, in _run_single_job_with_ui_loop
    result_builder = self.sa.run_job(job.id, ui, False)
  File "/snap/checkbox22/current/lib/python3.10/site-packages/plainbox/impl/decorators.py", line 142, in wrapper
    raise exc
  File "/snap/checkbox22/current/lib/python3.10/site-packages/plainbox/impl/decorators.py", line 136, in wrapper
    return func(*args, **kwargs)
  File "/snap/checkbox22/current/lib/python3.10/site-packages/plainbox/impl/session/assistant.py", line 1443, in run_job
    for cmd_part in self._restart_cmd_callback(
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/subcommands.py", line 312, in <lambda>
    lambda session_id: [shlex.join(respawn_cmd.append(session_id))]
  File "/snap/checkbox22/current/usr/lib/python3.10/shlex.py", line 320, in join
    return ' '.join(quote(arg) for arg in split_command)
TypeError: 'NoneType' object is not iterable

To Reproduce

1. Install checkbox22 snap 2.9 version
2. Run cold-boot-loop-reboot1 and warm-boot-loop-reboot1 tests in Stress Test Plan

Environment

• OS: Server Image 22.04
• Checkbox Type: Snap
• Checkbox Version: 2.9.0 2023-08-08 (473)
• Architecture: arm64

Relevant log output

No response

Additional context

No response

[pieqq]

I believe @baconYao is using a project-specific snap, but I confirm that this problem also happens with the generic checkbox snap.

To reproduce:

1. Install checkbox22 v2.9.0: sudo snap install checkbox22 --channel=latest/beta
2. Install checkbox generic snap: sudo snap install checkbox --channel=22.04/beta --classic
3. Launch checkbox: checkbox.checkbox-cli
4. Select IoT Client Certification for 22.04 classic images (Stress Tests) test plan
5. Deselect all the jobs by pressing d, then select only Perform cold reboot 1 from Cold-boot Stress Test category, and press t to start the session

Expected result: the system performs a poweroff and is restarted.

Actual result:

=============[ Running job 18 / 18. Estimated time left: 0:03:00 ]==============
---------------------------[ Perform cold reboot 1 ]----------------------------
ID: com.canonical.certification::cold-boot-loop-reboot1
Category: com.canonical.certification::stress-tests/cold-boot
Waiting for the system to shut down or reboot...
Traceback (most recent call last):
  File "/snap/checkbox22/current/bin/checkbox-cli", line 8, in <module>
    sys.exit(main())
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/checkbox_cli.py", line 163, in main
    subcmd.invoked(ctx)
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/subcommands.py", line 261, in invoked
    self._run_jobs(self.ctx.sa.get_dynamic_todo_list())
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/stages.py", line 375, in _run_jobs
    builder = self._run_single_job_with_ui_loop(
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/stages.py", line 189, in _run_single_job_with_ui_loop
    result_builder = self.sa.run_job(job.id, ui, False)
  File "/snap/checkbox22/current/lib/python3.10/site-packages/plainbox/impl/decorators.py", line 142, in wrapper
    raise exc
  File "/snap/checkbox22/current/lib/python3.10/site-packages/plainbox/impl/decorators.py", line 136, in wrapper
    return func(*args, **kwargs)
  File "/snap/checkbox22/current/lib/python3.10/site-packages/plainbox/impl/session/assistant.py", line 1443, in run_job
    for cmd_part in self._restart_cmd_callback(
  File "/snap/checkbox22/current/lib/python3.10/site-packages/checkbox_ng/launcher/subcommands.py", line 312, in <lambda>
    lambda session_id: [shlex.join(respawn_cmd.append(session_id))]
  File "/snap/checkbox22/current/usr/lib/python3.10/shlex.py", line 320, in join
    return ' '.join(quote(arg) for arg in split_command)
TypeError: 'NoneType' object is not iterable

I think this error was introduced with commit 40733bda61.

[pieqq]

The issue is from this change in subcommands.py:

            lambda session_id: [shlex.join(respawn_cmd.append(session_id))]

This is because shlex.join() expects an iterable, but list.append() actually returns None :)

I've got a fix for this, but I'm now trying to build a snap to test it on a local device.