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tox

tox is a generic virtual environment management and test command line tool, it aims to automate and standardize testing in Python. tox is part of a larger vision of easing the packaging, testing and release process of Python software (alongside pytest and devpi).

tox has influenced several other projects in the Python test automation space, such as Invoke, nox.

How to install it?

1. via pipx

It's recommended to use pipx to install tox into an isolated environment, run this command:

$ pipx install tox

2. via pip

Alternatively, you can install it within the global Python interpreter itself, run this command:

$ pip install --user tox

There are also other methods for tox installation, such as wheel, sdist. However, installation via setup.py is not recommended.

After the installation, validate it by running:

$ tox --help

How to use it?

tox is an environment orchestrator, it needs tox.ini configuration file to define what tools required to setup and execute on your project's test environment.

Except for the tox.ini configuration, tox supports pyproject.toml and setup.cfg as well. tox supports three configuration locations prioritized in the following order:

  1. tox.ini
  2. pyproject.toml
  3. setup.cfg

There are two types of configurations:

  • core settings [tox]
  • per-run environment settings [testenv] and [testenv:<envname>].

1. Create the virtual environment

Create a minimal tox.ini with the following configuration:

[tox]
skipsdist = true

Then run tox command:

$ tox
  py: OK (0.15 seconds)
  congratulations :) (0.20 seconds)

What's happened? Under the work directory, a .tox directory was created with the following contents:

.tox
└── py
    ├── bin
    │   ├── activate
    │   ├── activate.csh
    │   ├── activate.fish
    │   ├── activate.nu
    │   ├── activate.ps1
    │   ├── activate_this.py
    │   ├── pip
    │   ├── pip3
    │   ├── pip-3.10
    │   ├── pip3.10
    │   ├── python -> /usr/bin/python3
    │   ├── python3 -> python
    │   ├── python3.10 -> python
    │   ├── wheel
    │   ├── wheel3
    │   ├── wheel-3.10
    │   └── wheel3.10
    ├── lib
    │   └── python3.10
    ├── pyvenv.cfg
    └── tmp

5 directories, 18 files

You can see py is the default environment created by tox, and py version is what default in your machine.

You can control the environment creation by specifying the env_list or envlist option

[tox]
skipsdist = true
env_list = py310,py311,py312

Then run command $tox again, you can see these Python environments created under .tox directory,

.tox
├── py310
│   ├── bin
│   ├── lib
│   ├── pyvenv.cfg
│   └── tmp
├── py311
│   ├── bin
│   ├── lib
│   ├── pyvenv.cfg
│   └── tmp
└── py312
    ├── bin
    ├── lib
    ├── pyvenv.cfg
    └── tmp

12 directories, 3 files

What's about if you specify a Python version that does not exist on your system? For example, if I specify py39 in env_list and Python 3.9 is not installed on my machine, then tox would skip it and show the following information:

py39: skipped because could not find python interpreter with spec(s): py39
py39: SKIP ⚠ in 0.02 seconds

2. Activate the virtual environment

There is no need to activate the virtual environment with tox. tox is built on top of virtualenv aims to automate and standardize testing in Python.

When running the command

$ tox

It'll automatically start the command in virtual environment.

3. Manage Python packages

In the deps setting of [testenv] and [testenv:<envname>], you can specify the list of Python packages in Python environment hosting tox when running the tox command.

For example,

[tox]
requires =
    tox>=4
skipsdist = true
env_list = lint,type,py310,py311,py312

[testenv]
description = run unit tests
deps =
    pytest>=7
    pytest-sugar
commands =
    pytest {posargs:tests}

[testenv:lint]
description = run linters
skip_install = true
deps =
    black==22.12
commands = black {posargs:.}

[testenv:type]
description = run type checks
deps =
    mypy>=0.991
commands =
    mypy {posargs:src tests}

4. Deactivate the virtual environment

No need to deactivate the virtual environment.

5. Delete the virtual environment

tox does not provide methods to clean up the virtual environments after tox runs. The reason is that tox preserves the virtual environments as cache, the environments will be resused when you run tox next time, thus saving time.

If you do like to delete the virtual environments after tox runs, you could run this command manually:

$ rm -rf .tox

Or setup this command in your tox configuration,

[testenv]
...
allowlist_externals = rm
commands=
    pytest ...
    rm -rf {envdir}

For more information about tox, please refer to the official documentation.

Happy Coding!