bug#36430: mcron would benefit from a better way to test jobs

[Jesse Gibbons]

> My issue:

> Defined a mcron job in config.scm scheduled to run once a day,
> with a scheme expression. How do I test this?

Write the mcron job for a local installation of mcron first for
testing purposes, then move it into config.scm. That's how I do it.

> herd schedule mcron lists the job as merely a “Lambda expression”.
> I learned how to give it a descriptive name, but still there’s
> no script linked that I can run by hand.
>
> One major improvement would be to have:
>
> 1. `herd schedule mcron` lists jobs with some kind of id
> 2. `herd execute mcron <id>` runs the specific mcron job
>
> Or perhaps, any mcron job could be turned into a simple argument-less
> guile or shell script that’s shown in the schedule listing?
>
> Thoughts?
mcron --schedule=count gives you a listing of each scheduled job and
when it will next be run. I would expect "herd schedule mcron" runs
that command. I don't know about scheduling a function, but
if the scheduled job is a string it can be copied/pasted into a
terminal.

mcron is super buggy in my experience. If I power my laptop off
overnight it will skip all jobs scheduled for the day of the month,
even if they are scheduled for after I power it back on. And it doesn't
have a way to easily schedule for a given day of the week.