The Testing Goat

Obey the Testing Goat!

TDD for the Web, with Python, Selenium, Django, JavaScript and pals...

Test-Driven Development with Python, 2e, cover

The book

This is my book about Test-Driven-Development for web programming, published by the excellent O'Reilly Media.

There are a few ways you can read and support this book:

Obviously these are my favourite options! O'Reilly have been great, they deserve your support, and although I only get a small amount in royalties (about a dollar per sale if you're curious), it still pays for the occasional dinner out every month which I appreciate. Plus, real physical books are nice...

TIP: I don't recommend you use Google Play Books, or at least not their PDF version, it's horrible

Alternatively, or in the meantime, help yourself here! It's all free and CC-licenced (thanks O'Reilly!). I see this as a "try-before-you-buy" scheme, and I hope that if you enjoy it you'll buy a copy -- if not for yourself, then perhaps for a friend!

And do get in touch with comments, suggestions, corrections etc! [email protected]


New Book Excerpt: On Coupling and Abstractions

Being a discussion of abstractions, and how we can use them to reduce unnecessary coupling, make unit testing easier (or possible), and separate core logic from implementation details. Plus some discussion of functional-core-imperative-shell vs dependency injection.
Tue 03 September 2019 by Harry J.W. Percival

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Read the book

The book is available both for free and for money. It's all about TDD and Web programming. Read it here!

Reviews & Testimonials

"Hands down the best teaching book I've ever read""Even the first 4 chapters were worth the money""Oh my gosh! This book is outstanding""The testing goat is my new friend"Read more...


A selection of links and videos about TDD, not necessarily all mine, eg this tutorial at PyCon 2013, how to motivate coworkers to write unit tests, thoughts on Django's test tools, London-style TDD and more.

Old TDD / Django Tutorial

This is my old TDD tutorial, which follows along with the official Django tutorial, but with full TDD. It badly needs updating. Read the book instead!

Save the Testing Goat Campaign

The campaign page, preserved for history, which led to the glorious presence of the Testing Goat on the front of the book.