Test Driven Development: By Example

What the book is

Test Driven Development: By Example is Kent Beck's book on the practice he popularised: write a failing test, make it pass with the simplest code, then clean up. Published by Addison-Wesley in 2002, it runs to about 240 pages and remains the standard introduction to test-driven development (TDD).

What is inside

The book has three parts:

• A worked example in money arithmetic, built test by test in very small steps, so you see exactly how a design grows out of tests.
• A second worked example, building a small testing framework using the same method.
• Patterns for TDD, covering how to choose the next test, how to keep steps small, how to handle difficult dependencies, and how refactoring fits in.

The examples are in Java and Python, but the ideas apply to any language.

Why it matters with AI tools

When an AI tool writes code, the question is how you know it is right. TDD gives the strongest answer: a test you wrote first, that you watched fail, that now passes. It also fixes the most common weakness of AI-generated tests, which is that they describe whatever the code happens to do. If you write the first test yourself, you decide the behaviour; the tool then has a clear target and a check it can run by itself.

Is it worth your time?

Yes, if you have written some code and some tests and want a reliable method. It is short and readable, and the step-by-step style is best done with a keyboard, following along in your own language. You do not need to use strict TDD for everything afterwards; the value is in understanding why the loop works and when it helps most.

Prerequisites

Comfort in at least one programming language and some experience running tests. Absolute beginners will get more from it after a first testing tutorial.

What you can do after it

• Write a failing test before the code, and pick the next test well.
• Keep changes small enough that you always know what broke.
• Refactor confidently with tests as a safety net.
• Spot tests that could never fail.

How it fits the Coding with AI tools roadmap

The Sefism roadmap lists it in the tests-first stage, next to the free Obey the Testing Goat, as the book to read if you want the method from its source.

Common questions

Is it outdated? The tooling in the examples is old; the method is not.