tox-ignore-env-name-mismatch 0.1

A tox4 plugin for reusing a virtualenv across multiple test environments.

tox-ignore-env-name-mismatch

Reuse virtualenvs with multiple tox test environments.

If two environments have compatible specifications (basically, same deps) and use the same env_dir, installing this plugin and setting ignore_env_name_mismatch = true will allow tox to use the same underlying virtualenv for each test environment.

Usage

1. Install tox-ignore-env-name-mismatch in the same environment as tox.
2. Set ignore_env_name_mismatch = true to opt-out of recreating the virtualenv when the cached name differs from the current env name.

• To always use this plugin, specify requires = tox-ignore-env-name-mismatch in the [tox] section of tox.ini

Example

[tox]
envlist = py39,py310,py311,lint,format,types
requires = tox-ignore-env-name-mismatch

[testenv]
deps = pytest
commands = pytest {posargs}

[testenv:{lint,format,types}]
env_dir = {toxworkdir}{/}static
ignore_env_name_mismatch = true
deps =
    black
    flake8
    mypy
commands =
    lint: flake8 src tests
    format: black --check src tests
    types: mypy --strict src

see ./examples directory for a working example including the tox configuration above.

Why??

Typically this usage pattern is seen with "auxillary" environments that perform project operations, like linting, generating docs, or publishing packages. Using different testenv sections is a nice way to separate commands and passenv / setenv, but creating separate virtualenv that would otherwise use identical dependencies is both a waste of time and space.

In tox 3, it was possible to achieve this behavior (with a bug and some caveats) by simply having testenvs share an env_dir. In tox 4, this hackaround was properly fixed and now tox checks a cached {envdir}/.tox-info.json and recreates the virtualenv if the current testenv doesn't match what is cached.

This plugin allows a test environment to specifically opt-out of recreating the virtualenv when only the env_name.

This plugin only supports tox 4.

Motivation

People have been asking for this for at least 7 years and the core tox project is specifically not interested in supporting this use case in tox 4 (which is fine, that's what plugins are for).

• [tox-dev/tox#2788] Re-use of virtual environments across envs in tox4 [2022, Github]
• Reuse environment on Tox 4 [2022, StackOverflow]
• tox multiple tests, re-using tox environment [2019, StackOverflow]
• [tox-dev/tox#425] Ability to share tox environments within a project [2016, Github]
• Tox tricks and patterns#Environment reuse [2015, Blog]