Add testenv:dev to create development environment

[bhrutledge]

This is scratching an itch of mine. It feels a bit exotic, but I saw some prior art in virtualenv and build. I think it might be less exotic if we specified dependencies in extras_require or requirements files.

This allows VS Code to automatically detect my virtual environment, and use pytest/black/flake8 etc. directly from there while I'm editing individual files.

[sigmavirus24]

👍 Mostly because I had a tox -e venv which did 99.9% of this (it didn't print the executable version) and was removed at some point

[jaraco]

In my workflow, I have TOXENV=python, so tox --notest creates a development environment (and also a test environment for the default python), thus avoiding the added complication of orchestrating these environments and leading to a pretty simple tox config. I'm okay with this project creating arbitrarily complex tox configuration, but I'll personally be using testenv for the latest stable Python for 99% of my workflows.

[bhrutledge]

In my workflow, I have TOXENV=python, so tox --notest creates a development environment (and also a test environment for the default python)

I'm definitely in favor of simplifying things, but if I understand correctly, this only installs the [testenv]deps, and could also be accomplished with tox --devenv venv. I'd like one virtual environment with pytest, black, flake8, etc. This approach is also lightly documented by tox.

[sigmavirus24]

It's also relatively widespread in projects of any size and complexity (see also OpenStack and I believe Apache projects)

[bhrutledge]

@gaborbernat If you're feeling generous with your time, I'm curious what you think of this, as a maintainer of virtualenv and tox.

[gaborbernat]

Not sure what's the question, but I personally do prefer what this PR proposes. I've seen what @jaraco does, but I'd consider that a bit anti-pattern, though subjective at the end of the day, as it does not allow you to easily separate and recreate every python installation (could be just my experience, but version-specific bugs happen ever so often, and then it's good to quickly and easily reproduce them on your local machine).

[bhrutledge]

Not sure what's the question, but I personally do prefer what this PR proposes

Thanks @gaborbernat; no specific question. I was just wondering what your overall impression was, for example if you had any suggestions for improvement or caveats to be aware of.