Using Nox to automate your tests

• Article type: Tutorial
• OS needed: Any
• Programming language: Python

(Some references and examples were taken from the official documentation of nox)

Overview

Do you run tests when you write code? I do. That’s a great way to prevent terrifying mistakes on my projects. Some other times, I run linters to keep my codebase clean. One way or another, it is a good practice to use automation in our projects.

Sometimes, we want to use a lot of packages to test our code (for example: flake8, pytest, black, mypy, isort… and others), but we don’t want to run their commands, one by one… that’s boring!

Here is where Nox enters. It is a Python tool to automate tests and linters. Personally, I really like it to run tests on personal projects, but it’s not the only one. On this article, I would like to talk about this package, and how to set it up and run it. So, let’s begin.

Introducing Nox

Nox is a Python package created by Thea Flowers. You can get it using Pip:

pip install nox

Nox can help us to reduce steps to test the code. In most of the cases, if you use it, you will only have to run one command to test everything:

nox

(Sometimes, you will have to provide some options, but that’s all).

Another point in favor of Nox is the setup file it uses: a Python file named noxfile.py. It is simple and flexible, so you can implement Nox on every Python project you want!

Write a noxfile.py

import nox

@nox.session
def tests(session):
    session.install('pytest')
    session.run('pytest')

@nox.session
def lint(session):
    session.install('flake8')
    session.run('flake8', '--import-order-style', 'google')

This is a simple noxfile.py example, that I found on the official documentation.

First things first, you have to import Nox:

import nox

Each “step” can be declared on a function with the @nox.session decorator:

@nox.session
def tests(session):
    session.install('pytest')
    session.run('pytest')

@nox.session
def lint(session):
    session.install('flake8')
    session.run('flake8', '--import-order-style', 'google')

We have defined two sessions, tests and lint (actually the names doesn’t matter). On each session, we use session.install (to install the packages) and session.run (to run commands). On the example, we are telling Nox to install pytest and flake8, to run tests and linters with them.

Note: @nox.session accepts parameters, to customize the tests. See the reference here.

Running Nox

On the example, we are reducing steps to run exactly the same. Instead of running:

> pytest
    ...
> flake8 --import-order-style google
    ...

we only have to run the nox command:

> nox
    ...

You don’t even have to install pytest or flake8!

Going into a higher place

You don’t have limits when you use Nox… you can run code formatters, documentation builders, or even make a release using a single noxfile.py! You decide.

However, this is the most simple example I can post (he he he…). If you want to get a complete explanation, I recommend you to dive into the Nox documentation, or start with the Nox tutorial.

---

And this is where the article ends. I hope you like it, and maybe share this with more people. To go back to the main page of my website, press here.