Test-Driven Development with Kotlin

Introduction

The book «Test-Driven Development with Kotlin» (2021) by Cosimo Damiano Prete is a practical guide to implementing test-driven development (TDD) methodology in the Kotlin ecosystem. In an era where code quality and delivery speed are critical success factors, TDD offers a disciplined approach that allows you to write reliable, easily maintainable, and extensible code. This book is not just a collection of examples, but a full-fledged textbook that will guide the reader from the basics of TDD to building complex applications using modern architectural patterns and libraries.

What this book is about

The book consists of 12 chapters, logically divided into three parts. The first part introduces the basics of TDD and Kotlin: environment setup, writing the first tests, the «red-green-refactor» cycle. The second part delves into advanced techniques: mocks, stubs, testing asynchronous code, working with databases and REST APIs. The third part is dedicated to integrating TDD into real projects: Clean Architecture, dependency injection, CI/CD, and legacy code testing strategies.

Who this book is for

The book is aimed at developers already familiar with Kotlin or Java who want to systematically master TDD. It will be useful both for beginners in testing and for experienced engineers looking to organize their knowledge. A basic understanding of OOP and Kotlin syntax is sufficient for reading.

What the reader will learn

• TDD basics: the «red-green-refactor» cycle, FIRST principles, writing readable tests.
• Testing tools: JUnit 5, MockK, Kotest, AssertJ — setup and effective use.
• Testing different application layers: unit tests, integration tests, repository and controller tests.
• Working with asynchrony: testing coroutines, Flow, channels.
• Architectural patterns: Clean Architecture, ports and adapters, dependency injection via Koin or Dagger.
• Practical techniques: refactoring legacy code for tests, TDD for microservices, setting up CI with automatic test execution.
• Advanced techniques: parameterized tests, testing exceptions, working with time and randomness.

Strengths

The main advantage of the book is its practical focus. Each concept is supported by real code examples that can be immediately run and modified. The author consistently guides the reader from simple to complex, without overloading with theory. The chapter on testing coroutines deserves special attention — it is one of the best of its kind. Also worth noting is the emphasis on Clean Architecture: the book teaches not just how to write tests, but how to design a system so that it is testable from the start. The language is clear, the examples are neat and well-documented.

Who it is recommended for

The book will be useful for all Kotlin developers striving to improve the quality of their code. I especially recommend it to teams transitioning to a microservice architecture or implementing CI/CD. Beginners in TDD will find a structured introduction here, while experienced developers will find valuable recipes and best practices. If you write in Kotlin and want your applications to be reliable and your code clean, this book will be an excellent investment in professional development.