tox-poetry-installer

A Tox plugin for installing Tox environment dependencies using Poetry from the Poetry lockfile.

⚠️ This project is a very, very early prototype and should not be used in any production capacity.

Why would I use this?

The point of using a lockfile is to create reproducable builds. One of the main points of Tox is to allow a Python package to be built and tested in multiple environments. However, in the Tox configuration file the dependencies are specified with standard dynamic ranges and passed directly to Pip. This means that the reproducability a lockfile brings to a project is circumvented when running the tests.

The obvious solution to this problem is to add the dependencies required for testing to the lockfile as development dependencies so that they are locked along with the primary dependencies of the project. The only remaining question however, is how to install the dev-dependencies from the lockfile into the Tox environment when Tox sets it up. For very good reason Tox uses independent virtual environments for each environment a project defines, so there needs to be a way to install a locked dependency into a Tox environment.

This is where this plugin comes in.

Traditionally Tox environments specify dependencies and their corresponding versions inline in PEP-440 format like below:

[testenv]
description = Run the tests
deps =
  foo == 1.2.3
  bar >=1.3,<2.0
  baz

This runs into the problem outlined above: many different versions of the bar dependency could be installed depending on what the latest version is that matches the defined range. The baz dependency is entirely unpinned making it a true wildcard, and even the seemingly static foo dependency could result in subtly different files being downloaded depending on what's available in the upstream mirrors.

However these same versions, specified in the pyproject.toml file, result in reproducible installations when using poetry install because they each have a specific version and file hash specified in the lockfile. The versions specified in the lockfile are updated only when poetry update is run.

This plugin allows environment dependencies to be specified in the tox.ini configuration file just by name. The package is automatically retrieved from the lockfile and the Poetry backend is used to install the singular locked package version to the Tox environment. When the lockfile is updated, the Tox environment will automatically install the newly locked package as well. All dependency requirements are specified in one place (pyproject.toml), all dependencies have a locked version, and everything is installed from that source of truth.

Planned features

• Per-environment disabling (i.e. fallback to the default Tox installation backend)
• Detection of lockfile changes that trigger Tox environment recreation
• Tests