tox-poetry-installer

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

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

Documentation

• Installation
• Quick Start
• Reference and Usage
  • Config Option Reference
  • Error Reference
  • Example Config
• Known Drawbacks and Problems
• 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
• Poetry Dev-Dependencies Tox Plugin
• Poetry Tox Plugin
• Other Tox plugins

Installation

Add the plugin as a development dependency of a Poetry project:

~ $: poetry add tox-poetry-installer --dev

Confirm that the plugin is installed, and Tox recognizes it, by checking the Tox version:

~ $: poetry run tox --version
3.20.0 imported from .venv/lib64/python3.8/site-packages/tox/__init__.py
registered plugins:
    tox-poetry-installer-0.5.0 at .venv/lib64/python3.8/site-packages/tox_poetry_installer.py

If using Pip, ensure that the plugin is installed to the same environment as Tox:

# Calling the virtualenv's 'pip' binary directly will cause pip to install to that virtualenv
~ $: /path/to/my/automation/virtualenv/bin/pip install tox
~ $: /path/to/my/automation/virtualenv/bin/pip install tox-poetry-installer

Note: While it is possible to install this plugin using Tox's requires configuration option, it is not recommended. Dependencies from the requires option are installed using the default Tox installation backend which opens up the possibility of transient dependency problems in your automation environment.

Quick Start

To add dependencies from the lockfile to a Tox environment, add the option locked_deps to the environment configuration and list names of dependencies (with no version specifier) under it:

[testenv]
description = Some very cool tests
locked_deps =
    black
    pylint
    mypy
commands = ...

The standard deps option can be used in parallel with the locked_deps option to install unlocked dependencies (dependencies not in the lockfile) alongside locked dependencies:

[testenv]
description = Some very cool tests
locked_deps =
    black
    pylint
    mypy
deps =
    pytest == 6.1.1
    pytest-cov >= 2.10, <2.11
commands = ...

Alternatively, to quickly install all Poetry dev-dependencies to a Tox environment, add the install_dev_deps = true option to the environment configuration.

Note: Regardless of the settings outlined above, all dependencies of the project package (the one Tox is testing) will always be installed from the lockfile.

Reference and Usage

Config Option Reference

All options listed below are Tox environment options and can be applied to one or more environment sections of the tox.ini file. They cannot be applied to the global Tox configuration section.

NOTE: Environment settings applied to the main testenv environment will be inherited by child environments (i.e. testenv:foo) unless they are explicitly overridden by the child environment's configuration.

Option	Type	Default	Usage
locked_deps	Multi-line list	[]	Names of packages in the Poetry lockfile to install to the Tox environment. All dependencies specified here (and their dependencies) will be installed to the Tox environment using the version the Poetry lockfile specifies for them.
require_locked_deps	Bool	false	Indicates whether the environment should allow unlocked dependencies (dependencies not in the Poetry lockfile) to be installed alongside locked dependencies. If true then installation of unlocked dependencies will be blocked and an error will be raised if the deps option specifies any values.
install_dev_deps	Bool	false	Indicates whether all Poetry development dependencies should be installed to the environment. Provides a quick and easy way to install all dev-dependencies without needing to specify them individually.

Error Reference

• LockedDepVersionConflictError - Indicates that a locked dependency included a PEP-508 version specifier (i.e. pytest >=6.0, <6.1). Locked dependencies always take their version from the Poetry lockfile so specifying a specific version for a locked dependency is not supported.
• LockedDepNotFoundError - Indicates that a locked dependency could not be found in the Poetry lockfile. This can be solved by adding the dependency using Poetry.
• ExtraNotFoundError - Indicates that the Tox extras option specified a project extra that Poetry does not know about. This may be due to a misconfigured pyproject.toml or out of date lockfile.
• LockedDepsRequiredError - Indicates that an environment with require_locked_deps = true also specified unlocked dependencies using Tox's deps option. This can be solved by either setting require_locked_deps = false (the default) or removing the deps option from the environment configuration.

Example Config

[tox]
envlist = py, foo, bar, baz
isolated_build = true

# The base testenv will always use locked dependencies and only ever installs the project package
# (and its dependencies) and the two pytest dependencies listed below
[testenv]
description = Some very cool tests
require_locked_deps = true
locked_deps =
    pytest
    pytest-cov
commands = ...

# This environment also requires locked dependencies, but the "skip_install" setting means that
# the project dependencies will not be installed to the environment from the lockfile
[testenv:foo]
description = FOObarbaz
skip_install = true
require_locked_deps = true
locked_deps =
    requests
    toml
    ruamel.yaml
commands = ...

# This environment allows unlocked dependencies to be installed ad-hoc. Below, the "mypy" and
# "pylint" dependencies (and their dependencies) will be installed from the Poetry lockfile but the
# "black" dependency will be installed using the default Tox backend. Note, this environment does
# not specify "require_locked_deps = true" to allow the unlocked "black" dependency without raising
# an error.
[testenv:bar]
description = fooBARbaz
locked_deps =
    mypy
    pylint
deps =
    black
commands = ...

# This environment requires locked dependencies but does not specify any. Instead it specifies the
# "install_dev_deps = true" option which will cause all of the Poetry dev-dependencies to be
# installed from the lockfile.
[testenv:baz]
description = foobarBAZ
install_dev_deps = true
require_locked_deps = true
commands = ...

Known Drawbacks and Problems

• The following tox.ini configuration options have no effect on the dependencies installed from the Poetry lockfile (note that they will still affect unlocked dependencies):

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

• Tox will not automatically detect changes to the locked dependencies and so environments will not be automatically rebuilt when locked dependencies are changed. When changing the locked dependencies (or their versions) the environments will need to be manually rebuilt using either the -r/--recreate CLI option or the recreate = true option in tox.ini.

• There are a handful of packages that cannot be installed from the lockfile, whether as specific dependencies or as transient dependencies (dependencies of dependencies). This is due to an ongoing discussion in the Poetry project; the list of dependencies that cannot be installed from the lockfile can be found here. This plugin will skip these dependencies entirely, but log a warning when they are encountered.

Why would I use this?

Introduction

The lockfile is a file generated by a package manager for a project that records what dependencies are installed, the versions of those dependencies, and any additional metadata that the package manager needs 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 as a developer.

Poetry is a project dependency manager for Python projects, and so 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 dependencies in each environment. 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. This plugin extends the default Tox dependency installation behavior to support installing dependencies using a Poetry-based installation method that makes use of the dependency metadata from Poetry's lockfile.

The Problem

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

# from tox.ini
...

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

...

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

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

However there is a potential problem that could arise from each of these environment dependencies that would only appear in the Tox environment and not in the Poetry environment in use by a developer:

• 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 and then poetry add foo^1.2 to get the new version, but the Tox environment is left unchanged. The development environment, as defined 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 commands 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 and any errors that causes cannot be replicated 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, those dependencies' dependencies, and so on.

The Solution

This plugin allows dependencies specified in Tox environment take their version directly from the Poetry lockfile without needing an independent version to be specified in the Tox environment configuration. The modified version of the example environment given below appears less stable than the one presented above because it does not specify any versions for its dependencies:

# from tox.ini
...

[testenv]
description = Some very cool tests
require_locked_deps = true
locked_deps =
    foo
    bar
    baz

...

However with the tox-poetry-installer plugin installed the require_locked_deps = true setting means that Tox will install these dependencies from 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 versions of these dependencies, Tox will automatically install these new versions without needing any changes to the configuration.

Developing

This project requires a developer to have Poetry version 1.0+ installed on their workstation, 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.

The devel branch has the latest (potentially unstable) changes. The tagged versions correspond to the releases on PyPI.

• 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 for usage in production environments.

• 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 (#4)
• Add per-environment Tox configuration option to fall back to default installation backend.
• Add warnings when an unsupported Tox configuration option is detected while using the Poetry backend. (#5)
• Add trivial tests to ensure the project metadata is consistent between the pyproject.toml and the module constants.
• Update to use poetry-core and improve robustness of the Tox and Poetry module imports to avoid potentially breaking API changes in upstream packages. (#2)
• Find and implement a way to mitigate the UNSAFE_DEPENDENCIES issue in Poetry. (#6)
• Fix logging to make proper use of Tox's logging reporter infrastructure (#3)
• Add configuration option for installing all dev-dependencies to a testenv (#14)

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