This book is for machine learning professionals who want to be able to test the improvements to their algorithms in isolation and in an automated fashion. This book is for any data scientist who wants to get started in Test-Driven Development with minimal religion and maximum value. This book is not for someone who wants to learn state of the art Test-Driven Development. It is written with the idea that the majority of what can be learned from Test-Driven Development is remarkably simple. We will provide a relatively simple approach to it which the reader can choose to augment as they see fit.