Testing C# (.NET) Applications: From Unit Tests to Integration Tests

Testing is an integral part of professional software development. This book will be your reliable guide to the world of testing C# (.NET) applications. You will learn to write high-quality, maintainable, and effective tests that will save you hours of debugging and prevent regression errors.

What is this book about?

The book covers the full testing cycle of .NET applications — from basic unit tests to complex integration scenarios. You will get acquainted with modern frameworks (NUnit, xUnit, MSTest), libraries for creating stubs (Moq, NSubstitute), and approaches to organizing test infrastructure. Special attention is paid to practical aspects: how to properly structure tests, how to avoid brittle tests, and how to integrate testing into a CI/CD pipeline.

Who is this book for?

• Junior developers — master the basics of unit testing and learn to write your first tests.
• Middle developers — deepen your knowledge of mocking, dependency injection, and testing asynchronous code.
• Tech leads and architects — learn how to implement a testing culture in your team and organize the TDD (Test-Driven Development) process.

What will you learn?

• Basics of unit testing: AAA pattern (Arrange-Act-Assert), test isolation, working with fixtures.
• Advanced techniques: parameterized tests, exception testing, working with async/await.
• Mocking and stubs: creating stubs for external services, databases, HTTP clients.
• Integration testing: testing ASP.NET Core applications, Entity Framework, Web API.
• TDD in practice: how to write tests before implementation and get clean, testable code.
• Tools and best practices: Code Coverage, SonarQube, CI/CD with GitHub Actions and Azure DevOps.

Why should you read this book?

The author shares real-world experience, avoiding dry theory. Each chapter contains practical examples that you can immediately apply to your own projects. You will not just learn "how to write tests," but will also understand why certain approaches work better than others. The book is written in a lively style and is suitable both for self-study and for corporate training.

After reading, you will be able to confidently test any .NET applications, from console utilities to microservices on ASP.NET Core. Invest time in testing today — and your future projects will be more stable and of higher quality.