We have a Debian infrastructure with multiple web servers and a dedicated cron server where we are running unoconv as a service. The unoconv test in the admin menu failed consistently, which eventually turned out to be due to the file_exists() call in create_converted_document() returning false when the converted file had actually been created successfully. We worked out that 'touching' the file (and then checking its size rather than its existence) gives a much more reliable result in our case, although I can't offer an explanation as to why this is. However, this may conceivably be the case for some other people's setups too.

Whilst debugging this we also found a couple of other bugs, including one which results in the test file only needing to be successfully created once. After this Moodle just accesses the stored file and reports success every time (which makes debugging fun ). (Fixed in MDL-54647).

Another bug just results in the temp directory never being cleaned up after the testing process completes.

I've attached a patch containing a commit for each fix.