Testing Java Applications: From Unit Tests to Integration Scenarios

The book "Testing Java Applications" is a practical guide for Java developers who want to master modern testing approaches and learn to write reliable, maintainable tests. The author, Alexey Sokolov, shares years of experience in creating test scenarios for real projects, starting from the basics and ending with advanced techniques.

What is this book about?

The book covers the full testing cycle of Java applications:

• Basics of unit testing using JUnit 5 — test structure, annotations, assertion methods.
• Working with mocks and stubs using Mockito — dependency isolation, interaction verification.
• Integration testing — testing interactions with databases, REST APIs, and external services.
• Testing Spring Boot applications — using @SpringBootTest, @WebMvcTest, TestContainers.
• Test-Driven Development (TDD) — step-by-step code creation based on tests.
• Parameterized tests, exception testing, working with time and random data.

Who is this book for?

• Junior and Middle Java developers who want to systematize their knowledge of testing.
• Backend developers working with Spring Boot and microservice architecture.
• Anyone who wants to write code with minimal bugs and confidently refactor legacy projects.

What will you learn?

• How to organize a project's test architecture (AAA pattern, Fixture, Builder).
• How to write readable and independent tests that don't break with changes.
• How to test complex scenarios: asynchronous calls, multithreading, file operations.
• How to integrate tests into CI/CD pipelines (GitHub Actions, Jenkins).
• How to measure code coverage with JaCoCo and interpret reports.

The book contains numerous code examples, practical exercises, and checklists. All examples are available for download in a GitHub repository. After reading, you will be able to confidently implement testing in any Java project, reducing debugging time and increasing product stability.

"Testing Java Applications" is not just a collection of recipes, but a systematic approach to code quality that will help you become a more professional developer.