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The Hacker's Guide to Scaling Python

Setting Up Environments with tox

Explore how to use tox to automate Python testing environments, ensuring clean, isolated setups for unit and integration tests. Understand the challenges of orchestrating external services like memcached and learn best practices for reliable test execution in distributed systems.

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As you might already know, tox is a tool that automates building virtual Python environments. Those environments are isolated and straightforward to rebuild while having support for multiple Python versions at the same time in different environments.

Most of the time, tox is used to directly run unit tests of a program, with a file as simple as:

Python 3.8
[testenv]
deps=nose
commands=nosetests

Such a file makes sure that the tests are run in a clean Python environment with the right dependencies installed, as specified by your packaging tools.

Since it is possible to run any command by setting the commands parameter, it is easy to envision a system where you could start other services before running your tests. Therefore, a simplistic technique to run integration tests with memcached, for example, would be:

C++
[testenv]
commands=memcached -p 12345 &
        nosetests
...