Some people would like to set an environment variable manually on the command line, or something in pypi.rc or pip.conf, so they can tell pip to default to the new resolver #6536 #988 and test it more easily, without having to manually include --use-feature=2020-resolver each time. Example via Twitter:

It would be handy to be able to enable the new deps resolver via an env var. This would allow testing it in conjunction with tools such as poetry and pipenv.

@Julian in IRC logs suggested editing pip.conf and daturkel says this worked:

[install]
use-feature = 2020-resolver

We should decide whether we want to support this, and then if we do, we should add a line about it to the how-to-test docs.