Techniques and Insights to Deliver High-Quality, Maintainable Code
Test-Driven Development (TDD) is not only a way to test your code but a complete method of crafting software: How you think about code, the act of writing code, and how you continuously interact with your team's code. Essential Test-Driven Development guides you through writing tests before code, ensuring that every feature is clearly specified, thoroughly validated, and ready to meet evolving business needs.
This book shows how TDD can transform your development process by reducing costly bugs and empowering your team to deliver value with confidence. You'll see fewer defects with less worry about breaking existing features while implementing new ones. Developers can confidently reshape their code's internal design to accommodate new features and spend less time debugging.
The techniques and real-world examples in this book make TDD accessible to developers, managers, and product owners alike. Learn how to create a safety net of automated tests that protect your investment, accelerate delivery, and enable fearless innovation--whether working with legacy systems or new technologies. By adopting a test-driven mindset, you gain the skills to build software that's not only reliable today but is resilient to change tomorrow.
- Master the core TDD workflow of "Red, Green, Refactor" for iterative, quality-driven development
- Build and extend behaviors with clear, executable specifications
- Design for exceptional cases and edge conditions to prevent costly surprises
- Sustain a healthy, maintainable test suite with proven, long-term strategies
- Use test doubles to isolate dependencies and keep your tests fast and focused
- Apply TDD techniques to legacy codebases, making old software testable and reliable
- Understand the business impact of wholehearted TDD: fewer defects, faster feature delivery, and greater adaptability
- Explore how TDD principles extend across languages, frameworks, and modern agentic AI development
Take a practical step toward fewer bugs and smoother releases by exploring TDD at your own pace, with targeted examples and guidance you can actually use.
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Table of Contents:
Foreword xiii
Preface xix
Acknowledgments xxix
About the Author xxxi
Part I: Core Techniques 1
Chapter 1: Thinking Test-Driven 3
The Safety Net 4
Units of Behavior 4
Behavioral Boundaries 6
A Taste of TDD 9
The Future of Test-Driven Development 14
Summary 20
Chapter 2: Basic Moves 21
The TDD Flowchart 21
Thinking in Tests 23
Three Basic Techniques 26
Requests, Tasks, and a To-Do List 26
Exercise Walk-Through 30
Summary 45
Chapter 3: Build upon Existing Behavior 47
Next Steps 47
Improving the Tests 53
Refactoring the Tests 55
Removing the Symptomless Defect 57
Triangulating Away Side Effects 60
A Picture Is Worth a Thousand Words 62
Combining Behaviors 66
Summary 71
Chapter 4: Exceptional Behaviors 73
Raising/Throwing 73
A Test That Passes When the Code "Fails" 75
External Exceptions 77
Summary 78
Chapter 5: Sustaining a Test-Driven Practice 79
Attributes of a Good Unit Test 80
Where to Start 83
What to Test 88
When Code Is Difficult to Test 96
Test Smells and Refactorings 97
Other Common Testing Challenges 136
How to Test a Private
Summary 138
Part II: Ancillary Practices 139
Chapter 6: Test Doubles 141
The Trouble with Dependencies 142
A Test Double Taxonomy 143
Additional Recommendations 153
Summary: Use with Care 160
Chapter 7: Testing Legacy Code 163
Characterization Testing 165
Other Considerations 177
Introduce Virtualizing Proxy 180
Summary: The Complete Toolbox 186
Part III: Return on Investment 189
Chapter 8: The Black Swans 191
The Agilist's Dilemma 192
The Three Levels of Value 193
The Black Swan User Stories 195
Taming the Black Swans 204
Summary 205
Appendix: Exercises 207
Index 213
