Testing JavaScript (Node.js) Applications

The book "Testing JavaScript (Node.js) Applications" is a practical guide that will help you master all aspects of automated testing of server-side code in Node.js. From basics to advanced techniques — you will learn to write reliable tests that will save hours of debugging and make your code resistant to regressions.

What is this book about?

The book covers the full testing cycle of modern Node.js applications:

• Unit testing — isolating functions and modules using Mocha, Jest, and Chai.
• Integration testing — checking interactions with databases (MongoDB, PostgreSQL) and external APIs.
• Functional and E2E testing — simulating HTTP requests with Supertest and Playwright.
• Mocking and Stubbing — replacing dependencies with Sinon.js and Test Doubles.
• CI/CD integration — setting up automatic test execution in GitHub Actions and GitLab CI.
• Testing asynchronous code — promises, async/await, timers, and events.

Who is this book for?

• Junior developers who want to learn to write their first tests and understand their value.
• Middle/Senior developers striving to systematize knowledge and implement TDD/BDD in their team.
• QA engineers transitioning from manual to automated testing.
• Team leads and architects planning a testing strategy for a project.

What will you learn?

After reading the book, you will be able to:

• Choose the right type of tests for each part of the application.
• Set up a test environment: isolated databases, fixtures, environment variables.
• Write readable and maintainable tests using patterns (Arrange-Act-Assert, Given-When-Then).
• Integrate tests into a CI/CD pipeline and obtain coverage metrics (Istanbul/NYC).
• Test Express/Koa applications, WebSocket servers, and microservices.
• Avoid common mistakes: brittle tests, false positives, slow suites.

The book contains over 30 practical examples and ready-made projects that can be downloaded and run. All examples are relevant for Node.js 18+ and the latest versions of frameworks. Suitable for both self-study and corporate training.

Make your code predictable and reliable — start testing the right way!