Option to set the default distribution algorithm

[DavideCanton]

Hi, I have the following scenario:

• I have some tests that need to be run in the same worker due to the fact they use a shared object (I know it's not very idiomatic for unit tests, but it is really the simpler way to check what I need to check)
• I saw the --dist loadgroup option, but unfortunately it is not the default, so I should remember to specify every time the command line option
• I can't add it to the addopts setting since it errors if I don't specify either -n or -tx, and I want to be able to choose to run the tests the standard way too.

What could work for me is a setting to set the default algorithm to use when --dist is not specified, so that:

• if I run pytest standalone, it doesn't run in parallel
• if I run pytest -n auto, it uses the algorithm specified in the setting
• if I run pytest -n auto --dist loadfile, it overrides the setting with the loadfile algorithm.

[antazoey]

I need this as well.

Something like this would be nice:

[pytest.xdist]
dist = "loadscope"

such that whenever -n is used, it will automatically use loadscope distribution. Like the issue author states, it helps so I don't have to remember to use --dist loadscope because I have some tests scattered about that share a resource (a special, complicated process running).

[DavideCanton]

I could try setting up a PR if someone is interested in merging it

[nicoddemus]

I don't think we need a separate option, I would prefer if we can make it possible to set --dist X using addopts, without erroring out if -n is not passed too.

[antazoey]

I don't think we need a separate option, I would prefer if we can make it possible to set --dist X using addopts, without erroring out if -n is not passed too.

This works for me

[DavideCanton]

I don't think we need a separate option, I would prefer if we can make it possible to set --dist X using addopts, without erroring out if -n is not passed too.

How I could run pytest without erroring if -n is not passed?

[nicoddemus]

I think it should be possible to implement that (can't look at the code right now).

[DavideCanton]

It can be implemented since we had to do it by using pytest hooks, but it's quite messy since you have to dig deep inside how the workers read the options

[nicoddemus]

Opened #851. 👍