Testing Kotlin Applications: From Unit Tests to E2E

The book "Testing Kotlin Applications" is a comprehensive guide that will help you master all levels of testing in the Kotlin ecosystem. Whether you are writing a backend with Ktor, a mobile application on Android, or a multiplatform project, this book will become your reliable assistant.

What this book is about

The author consistently guides the reader from basic concepts to complex testing scenarios. You will learn:

• How to set up a test environment with JUnit 5, Kotest, and Spek
• Principles of working with mocks and stubs using MockK (a specialized framework for Kotlin)
• Features of testing coroutines and Flow
• Methods for testing DI containers (Koin, Dagger Hilt)
• Integration testing of databases with Exposed and Room
• Writing E2E tests for REST APIs and UI components
• TDD (Test-Driven Development) practices with real-world examples

Who this book is for

This book will be useful for:

• Beginner Kotlin developers who want to lay the right foundations for testing
• Android developers transitioning from Java to Kotlin
• Backend developers using Ktor or Spring Boot with Kotlin
• Team Leads and architects implementing a quality culture in their team

What you will gain

After reading the book, you will be able to:

• Write clean, isolated unit tests using mocks and spies
• Test asynchronous code with coroutines without headaches
• Automate business logic verification and error handling
• Integrate tests into a CI/CD pipeline (GitHub Actions, GitLab CI)
• Generate code coverage reports and analyze them

Each chapter contains practical examples ready for use. The code from the book is available on GitHub and is fully compatible with the latest versions of Kotlin (1.9+).

"Testing Kotlin Applications" is not just theory, but a set of proven practices that will save you hours of debugging and make your code more reliable. Ideal for those who value quality and want to write software that can be trusted.