Comment 1 for bug 1975711

I was able to resolve this on my machine by using pip-tools' pip-compile[1] to pin the versions of dependencies prior to running tox. This means that the tox virtualenv generation doesn't try to resolve all cross-dependencies (getting stuck along the way), and instead uses the pinned versions defined by pip-compile.

Doing this means slightly refactoring how requirements are defined in the project. I'm working on a draft patch to show what that would look like and will create a review soon.

[1] https://github.com/jazzband/pip-tools