fe_test: add test for syslog feature

[freddy77]

The syslog feature allows to run a program and redirect its output/error stream to system log. It's triggered passing syslog_stdout argument to Forkhelpers functions like execute_command_get_output.
To test this feature use a small preload library to redirect syslog writing.
This allows to test program without changing it.
The log is redirected to /tmp/xyz instead of /dev/log. The name was chosen to allow for future static build redirection.
The C program is used only for the test, so the code style take into account this (specifically it does not try to handle all redirect situation and all error paths).

[lindig]

Where would we use this and what is the current pain point?

[edwintorok]

there is a commented out stub for openlog in syslog_stubs.c, could we use that to redirect output for testing purposes?
LOG_PERROR would redirect messages to stderr which can be intercepted with a pipe. Not sure whether that'd be more or less convenient than intercepting with LD_PRELOAD.

[freddy77]

Okay, fixing the race, it's a problem with the test not ignoring logs from the daemon. Why it didn't happen before, I have no idea.

[freddy77]

there is a commented out stub for openlog in syslog_stubs.c, could we use that to redirect output for testing purposes? LOG_PERROR would redirect messages to stderr which can be intercepted with a pipe. Not sure whether that'd be more or less convenient than intercepting with LD_PRELOAD.

I don't want to change a line of the code beside the test, that's why I used that method.

[freddy77]

Where would we use this and what is the current pain point?

What's "this" in your sentence ? Not clear what do you mean by pain point, are you asking me what's the importance of testing ? I suppose not. Not a rhetorical question, just I don't understand the question. That part of code was not tested so I'm adding a test.

[freddy77]

Removed the race condition.
Rewrote the commit message, it was confusing, to say the least. My first though was "who wrote this?".

[freddy77]

ping