Hi, it is probably common (enough) that when using xdist people are running pytest multiple time(s), I think @nicoddemus even mentioned he does this, we do in work similar like:

# multiple jenkins stages & pytest invocations are involved in one 'CI run'
pytest -m parallel and not isolated --debug
pytest -m isolated --debug

By default --debug opens the pytestdebug.log file with w which means collecting artifacts later to assist with debugging when using a CI system like jenkins for example is often problematic as you will only receive the isolated runs debug logs here

I propose one of the following:

• --debug-file=debug1.log (I think keeping the same root dir here but allowing unique names could be beneficial)
• --debug-append which appends (a) to the file if it already exists

Thoughts? I will PR if you think its got any merit