tox

tox is a command-line testing automation tool that manages Python virtual environments and executes tests across multiple Python versions and configurations. It allows developers to define standardized test environments and run tests reliably across different platforms.

Key Features

• Multi-Environment Testing: Creates and manages separate virtual environments for different Python versions and configurations
• Configuration as Code: Uses a tox.ini file for declarative test environment setup
• CI Integration: Commonly used in continuous integration pipelines
• Parallel Execution: Can run test environments concurrently with --parallel
• Dependency Management: Handles installation of test dependencies per environment
• Platform Support: Works across Windows, macOS, and Linux

Example Configuration

This configuration will run pytest on Python 3.7 through 3.10.

[tox]
envlist = py37,py38,py39,py310
isolated_build = True

[testenv]
deps =
    pytest>=6.0
    pytest-cov>=2.0
commands =
    pytest {posargs:tests}

Pros

• Industry-standard for Python library testing
• Well-documented with extensive community support
• Integrates smoothly with CI/CD pipelines
• Ensures consistent test environments
• Supports complex test matrices

Cons

• Configuration can be complex for advanced use cases
• Slower than newer alternatives like nox
• INI format less flexible than Python-based configuration
• Can consume significant disk space with multiple environments

When to Use tox

Consider using tox when:

• Testing libraries that support multiple Python versions
• Need for standardized test environments across team members
• Complex testing requirements involving different dependency sets
• Continuous integration requires matrix testing

Learn More

• tox Documentation
• Python Testing with tox
• tox GitHub Repository
• tox-uv