Handy API to know information about master/slaves from session

[smarie]

As mentioned in smarie/python-pytest-harvest#36 (and discussed already with @nicoddemus in smarie/python-pytest-harvest#32) it would be great to have an elegant API to answer these simple questions:

• get_xdist_worker_id(session): would return session.config.slaveinput['slaveid'] or raise an exception if this not an xdist worker
• is_xdist_worker(session): would return True if this is an xdist worker, False otherwise
• is_xdist_master(session): would return True if this is the xdist master, False otherwise (important: this would return False when distribution has not been activated and "normal" pytest has been run on a single process)

Would you like a PR for this ?

When/if this API is done, we should not forget to post the answer on this SO question

[smarie]

Implementation note : is_xdist_master could rely on the second environment variable listed in the doc:

• PYTEST_XDIST_WORKER: the name of the worker, e.g., "gw2".
• PYTEST_XDIST_WORKER_COUNT: the total number of workers in this session, e.g., "4" when -n 4 is given in the command-line.

PYTEST_XDIST_WORKER_COUNT seems to be a viable way to disambiguate between no distribution and master node with distribution. To check

[smarie]

Update: actually a better way was just to check at request_or_session.config.option.dist != "no".

I'll push a PR in a minute