Follow up to #64, based on suggestion in #64 (comment):

The agent log file can go to tmp. We can monitor this one for potential errors. I wonder if we can do the same for metricbeat and filebeat logs.

... it's a rather a nice-to-have feature to also observe programmatically logs of elastic-agent, filebeat and metricbeat while testing. Many configuration errors are reported deep down by filebeat or metricbeat's internals.
Logs can be collected in the same single directory and exported as volume.