test_config: use native tmp_path pytest fixture

[sbesson]

Fixes #42 (see https://github.com/ome/omero-py/runs/6574741655?check_suite_focus=true for the latest occurence of this bug)

The current test_config implementation makes use of the temporary file utility the omero.util.temp_files module. This implementation is not thread safe when running the pytest in a distributed manner as the username ("runner") used for the based directory is the same for all workers.
This creates a potential race condition when from omero.util.temp_files import create_path is invoked concurrently as multiple workers might attempt to use os.makedirs to create the same omero_runner directory.

This PR updates the test implementation to use pytest native tmp_path fixture. Each temporary directory should be unique within the scope of the test so there should be no conflict between workers.

[joshmoore]

Interesting & good find. I do wonder about the possible issues that create_path's non-thread-safety might cause.

This has been in for some time and things are green, 👍

[sbesson]

I do wonder about the possible issues that create_path's non-thread-safety might cause.

Hopefully the impact should be limited as the issue is related to the creation of the parent directory <OMERO_TEMPIR>/omero_<user>. Since this parent directory is not cleaned up by the library, I think we are dealing with a one-off race condition per user. If this was causing problems with the library usage (rather than the tests), a possible workaround would be to pass exist_ok=True to os.makedirs in TempFileManager.__init__