There are a few repositories sharing the same environment dir to avoid recreating an environment when it shares the same python version and set of dependencies as another environment but differs in the command being run. One such use case is in integration/quibble.git which has cover and integration env which are the same as a py3-unit env albeit with a different command. Here is a summary of the tox.ini:
envdir = # tox v3 provisionining would fail with: # ConfigError:envdir must not equal toxinidir .tox: {toxworkdir}/.pkg py3-unit: {toxworkdir}/venv-py3 py3-lint: {toxworkdir}/venv-lint-py3 check: {toxworkdir}/venv-py3 black: {toxworkdir}/black integration: {toxworkdir}/venv-py3 cover: {toxworkdir}/venv-py3 venv: {toxworkdir}/venv-py3
That has however never been supported in tox 3 ( https://github.com/tox-dev/tox/issues/425#issuecomment-801296002 ) and is explicitly not supported in tox v4 ( https://github.com/tox-dev/tox/issues/2788 ). The comparison is done based on the testenv name (py3-unit, cover, integration) and the type of runner (VirtualEnvRunner). Any mismatch cause a recreation, here is an example with tox v4 without any .tox:
check: install_deps> python -I -m pip install '.[test]'
...
check: install_package_deps> python -I -m pip install 'GitPython~=3.1.0' PyYAML extras requests six
check: install_package> python -I -m pip install --force-reinstall --no-deps /home/hashar/projects/integration/quibble/.tox/.tmp/package/1/quibble-1.5.6.post5+git.1fe36f58.dirty.tar.gz
check: OK ✔ in 19.41 seconds
...
py3-unit: recreate env because env type changed from {'name': 'check', 'type': 'VirtualEnvRunner'} to {'name': 'py3-unit', 'type': 'VirtualEnvRunner'}
py3-unit: remove tox env folder /home/hashar/projects/integration/quibble/.tox/venv-py3
py3-unit: install_deps> python -I -m pip install '.[test]'
py3-unit: install_package_deps> python -I -m pip install 'GitPython~=3.1.0' PyYAML extras requests sixSo that even if check and py3-unit shares the same basepython, type of runner and set of dependencies, a new venv gets created since the names mismatch.
There is a plugin to filter out the test environment name from the configuration when doing the comparison: tox-ignore-env-name-mismatch. Then I guess it is easier to stop mangling with the environment directories and have one directory per environment. That causes some more disk space to be used, but speed wise the dependencies would be installed from the wheel cache so that should be rather fast.
That also let me get rid of a tox v3 back compatibility hack to provision tox v4 in a .pkg/.package env:
envdir = .tox = {toxworkdir}/.pkg