Test-Driven Development with Python: Obey the Testing Goat: Using Django, Selenium, and JavaScript

Testing often feels like a chore—until it becomes the backbone of your development process. Harry J.W. Percival’s third edition of Test-Driven Development with Python turns TDD into a practical adventure, using a real web application built with Django, Selenium, and JavaScript. The famous “testing goat” mantra appears throughout: obey the testing goat—write a test, watch it fail, then make it pass.

Why This Edition Matters

This version is thoroughly modernized, running on Python 3.14 and Django 5. It adds a preface on TDD in the age of AI, addressing how automated testing still fits into the workflow of today’s developer. The book doesn’t just preach TDD; it walks through a complete project, from first functional test to deployment.

What You’ll Build and Practice

The core example is a to-do list application, but that simple premise becomes a vehicle for learning professional web development habits. You’ll write functional tests with Selenium, unit tests with the standard library’s unittest module, and Django’s testing tools. The book covers test isolation, dealing with asynchronous browser behavior, and reading tracebacks effectively.

• Write functional tests before writing code
• Use unit tests for core logic and database interactions
• Mock external systems to isolate tests
• Package and run the application with Docker
• Set up continuous integration and automated deployments
• Add test-driven JavaScript to the frontend

Beyond Basic TDD

Percival doesn’t stop at testing syntax. He explores refactoring, design decisions, and the test-code-refactor cycle in depth. You’ll see how to avoid brittle tests, test behavior rather than implementation, and use tests to guide architecture. Chapters on layout and styling even show how to test what matters without overtesting cosmetics.

For Developers Who Want Reliable Code

If you’re a professional developer or moving into web development with Python, this book gives you the confidence to change code without fear. The hands-on approach works whether you’re new to Django or want to deepen your testing practice. The consistent “obey the testing goat” runs through each step, reminding you to test first, refactor with confidence, and keep the build green.

Grab your copy and bring a little order to your development chaos—one test at a time. 🐐