Test-Driven Development: By Example

This is the book that started it all. Kent Beck's Test-Driven Development: By Example isn't just a book about testing—it's a manifesto for how to think about software development. Beck introduces TDD not as a technique, but as a way to reduce fear in programming. When you write tests first, you're not just verifying code works; you're designing the interface, clarifying requirements, and building confidence incrementally. The book is structured in three parts: The Money Example walks you through building a multi-currency system step-by-step, showing how tests drive design decisions. The xUnit Example is brilliant—you build a testing framework using TDD itself, which teaches you both how to write tests and how testing frameworks work under the hood. The Patterns section distills the lessons into reusable practices. What makes this book timeless is that it's not about tools or languages—it's about the rhythm of red-green-refactor, the discipline of writing failing tests first, and the confidence that comes from knowing your code works because you've proven it. In the age of AI code assistants, this book becomes even more critical: when AI generates code, TDD ensures you're not just accepting what it produces—you're verifying it meets your actual requirements. The examples are in Java, but the principles apply to any language. This is required reading for any serious developer.