In modern Python development, maintaining compatibility across multiple Python versions is super critical, especially for libraries and tools that target a diverse user base. Here, we explore how to use Tox and Nox, two powerful tools for Python test automation, to validate projects across multiple Python versions. Using a concrete project as an example, we'll walk through setting up multi-version testing, managing dependencies with Poetry, and using Pytest for unit testing.

Automating tests across Python versions ensures your project remains robust and reliable in diverse environments. Multi-version testing can:

Both tools aim to simplify testing across multiple Python versions, but their approaches make them suited for different needs.

Let's set up a project named to demonstrate the integration of Tox, Nox, Poetry, and Pytest. The project includes simple addition and subtraction functions, tested across Python versions 3.8 to 3.13.

The calculator module contains two basic functions:

Run the following commands to install dependencies and create a virtual environment:

Tox automates testing across Python versions using isolated virtual environments. The configuration is declarative and resides in a file, testing the app with Python versions from 3.8 to 3.13:

Tox will automatically create environments for each Python version and execute the suite in isolation.

For more dynamic configurations, use Nox. Its Python-based scripts allow complex logic and custom workflows and test the app with Python versions from 3.8 to 3.13:

Nox offers flexibility for customizing workflows, such as conditional dependency installation or environment-specific configurations.

Automate the testing process further by integrating Tox and/or Nox into a CI/CD pipeline.

For example, a GitHub Actions workflow can look like this:

As an option, the following GitLab CI/CD pipeline runs tests across multiple Python versions:

Keep in mind that you run either Tox or Nox in your project, not both, since they have similar goals.

By combining Tox or Nox with Poetry and Pytest, you can achieve seamless multi-version test automation for Python projects. Whether you prefer the declarative approach of Tox or the programmable flexibility of Nox, these tools ensure your code is validated across a wide range of Python environments. That approach is especially useful for shared libs projects and multi-user environments projects.

For the complete example, check the project repository GitHub: tox-nox-python-tests.

This project uses Tox, Nox, Poetry, and Pytest for test automation. For detailed documentation, refer to: