tox-poetry-installer

A plugin for Tox that allows test environment dependencies to be installed using Poetry using its lockfile.

⚠️ This project is alpha software and should not be used in a production capacity ⚠️

Documentation

• Installation and Usage
• Limitations
• Why would I use this? (What problems does this solve?)
• Developing
• Contributing
• Roadmap
  • Path to Beta
  • Path to Stable

Related resources:

• Poetry Python Project Manager
• Tox Automation Project
• Tox plugins

Installation and Usage

1. Install the plugin from PyPI:

poetry add tox-poetry-installer --dev

2. Remove all version specifications from the environment dependencies in tox.ini:

# This...
[testenv]
description = My cool test environment
deps =
    requests >=2.19,<3.0
    toml == 0.10.0
    pytest >=5.4

# ...becomes this:
[testenv]
description = My cool test environment
deps =
    requests
    toml
    pytest

3. Run Tox with the --recreate flag to rebuild the test environments:

poetry run tox --recreate

4. 💸 Profit 💸

Limitations

• In general, any command line or INI settings that affect how Tox installs environment dependencies will be disabled by installing this plugin. A non-exhaustive and untested list of the INI options that are not expected to work with this plugin is below:

  • install_command
  • pip_pre
  • downloadcache (deprecated)
  • download
  • indexserver
  • usedevelop
  • extras

• When the plugin is enabled all dependencies for all environments will use the Poetry backend provided by the plugin; this functionality cannot be disabled on a per-environment basis.

• Alternative versions cannot be specified alongside versions from the lockfile. All dependencies are installed from the lockfile and alternative versions cannot be specified in the Tox configuration.

Why would I use this?

Introduction

The lockfile is a file generated by a package manager for a project that lists what dependencies are installed, the versions of those dependencies, and additional metadata that the package manager can use to recreate the local project environment. This allows developers to have confidence that a bug they are encountering that may be caused by one of their dependencies will be reproducible on another device. In addition, installing a project environment from a lockfile gives confidence that automated systems running tests or performing builds are using the same environment that a developer is.

Poetry is a project dependency manager for Python projects, and as such it creates and manages a lockfile so that its users can benefit from all the features described above. Tox is an automation tool that allows Python developers to run tests suites, perform builds, and automate tasks within self contained Python virtual environments. To make these environments useful, Tox supports installing per-environment dependencies. However, since these environments are created on the fly and Tox does not maintain a lockfile, there can be subtle differences between the dependencies a developer is using and the dependencies Tox uses.

This is where this plugin comes into play.

By default Tox uses Pip to install the PEP-508 compliant dependencies to a test environment. A more robust way to do this is to install dependencies directly from the lockfile so that the version installed to the Tox environment always matches the version Poetry specifies. This plugin overwrites the default Tox dependency installation behavior and replaces it with a Poetry-based installation using the dependency metadata from the lockfile.

The Problem

Environment dependencies for a Tox environment are usually done in PEP-508 format like the below example

# tox.ini
...

[testenv]
description = Some very cool tests
deps =
    foo == 1.2.3
    bar >=1.3,<2.0
    baz

...

Perhaps these dependencies are also useful during development, so they can be added to the Poetry environment using this command:

poetry add foo==1.2.3 bar>=1.3,<2.0 baz --dev

However there are three potential problems that could arise from each of these environment dependencies that would only appear in the Tox environment and not in the Poetry environment:

• The foo dependency is pinned to a specific version: let's imagine a security vulnerability is discovered in foo and the maintainers release version 1.2.4 to fix it. A developer can run poetry remove foo && poetry add foo^1.2 to get the new version, but the Tox environment is left unchanged. The developer environment specified by the lockfile is now patched against the vulnerability, but the Tox environment is not.

• The bar dependency specifies a dynamic range: a dynamic range allows a range of versions to be installed, but the lockfile will have an exact version specified so that the Poetry environment is reproducible; this allows versions to be updated with poetry update rather than with the remove and add used above. If the maintainers of bar release version 1.6.0 then the Tox environment will install it because it is valid for the specified version range, meanwhile the Poetry environment will continue to install the version from the lockfile until poetry update bar explicitly updates it. The development environment is now has a different version of bar than the Tox environment.

• The baz dependency is unpinned: unpinned dependencies are generally a bad idea, but here it can cause real problems. Poetry will interpret an unbound dependency using the carrot requirement but Pip (via Tox) will interpret it as a wildcard. If the latest version of baz is 1.0.0 then poetry add baz will result in a constraint of baz>=1.0.0,<2.0.0 while the Tox environment will have a constraint of baz==*. The Tox environment can now install an incompatible version of baz that cannot be easily caught using poetry update.

All of these problems can apply not only to the dependencies specified for a Tox environment, but also to the dependencies of those dependencies, and so on.

The Solution

This plugin requires that all dependencies specified for all Tox environments be unbound with no version constraint specified at all. This seems counter-intuitive given the problems outlined above, but what it allows the plugin to do is offload all version management to Poetry.

On initial inspection, the environment below appears less stable than the one presented above because it does not specify any versions for its dependencies:

# tox.ini
...

[testenv]
description = Some very cool tests
deps =
    foo
    bar
    baz

...

However with the tox-poetry-installer plugin installed this instructs Tox to install these dependencies using the Poetry lockfile so that the version installed to the Tox environment exactly matches the version Poetry is managing. When poetry update updates the lockfile with new dependency versions, Tox will automatically install these new versions without needing any changes to the configuration.

All dependencies are specified in one place (the lockfile) and dependency version management is handled by a tool dedicated to that task (Poetry).

Developing

This project requires Poetry-1.0+, see the installation instructions here.

# Clone the repository...
# ...over HTTPS
git clone https://github.com/enpaul/tox-poetry-installer.git
# ...over SSH
git clone git@github.com:enpaul/tox-poetry-installer.git

# Create a the local project virtual environment and install dependencies
cd tox-poetry-installer
poetry install

# Install pre-commit hooks
poetry run pre-commit install

# Run tests and static analysis
poetry run tox

Contributing

All project contributors and participants are expected to adhere to the Contributor Covenant Code of Conduct, Version 2.

• To report a bug, request a feature, or ask for assistance, please open an issue on the Github repository.
• To report a security concern or code of conduct violation, please contact the project author directly at ethan dot paul at enp dot one.
• To submit an update, please fork the repository and open a pull request.

Roadmap

This project is under active development and is classified as alpha software, not yet ready usage in production systems.

• Beta classification will be assigned when the initial feature set is finalized
• Stable classification will be assigned when the test suite covers an acceptable number of use cases

Path to Beta

• Verify that primary package dependencies (from the .package env) are installed correctly using the Poetry backend.
• Support the extras Tox configuration option
• Add per-environment Tox configuration option to fall back to default installation backend.
• Add detection of a changed lockfile to automatically trigger a rebuild of Tox environments when necessary.
• Add warnings when an unsupported Tox configuration option is detected while using the Poetry backend.
• Add trivial tests to ensure the project metadata is consistent between the pyproject.toml and the module constants.
• Update to use poetry-core Tox configuration option) and improve robustness of the Tox and Poetry module imports to avoid potentially breaking API changes in upstream packages.

Path to Stable

Everything in Beta plus...

• Add tests for each feature version of Tox between 2.3 and 3.20
• Add tests for Python-3.6, 3.7, and 3.8
• Add Github Actions based CI
• Add CI for CPython, PyPy, and Conda
• Add CI for Linux and Windows