What Is Unit Testing?

Unit testing means checking that small, individual pieces of your code—called units—work as expected. In a Spring Boot application, a unit is usually a single method or class, such as a service or a utility function. You write unit tests to make sure each unit returns the correct output for a given input.

Why Unit Testing Matters in Spring Boot

Spring Boot applications can grow quickly and become complex. Unit tests help you:

• Catch bugs early before they reach production;
• Save time by finding problems close to where they start;
• Refactor or change code with confidence, knowing tests will alert you if something breaks;
• Document how code is supposed to work for future developers.

When you unit test your Spring Boot code, you make sure each part works on its own. This leads to more reliable and maintainable applications.

Basic Principles of Unit Testing

Follow these principles to write effective unit tests:

• Test one thing at a time: each test should focus on a single method or class;
• Isolate the unit: avoid calling databases, web servers, or other systems in unit tests;
• Use predictable inputs and outputs: always know what you expect from each test;
• Make tests repeatable: a test should always give the same result, every time you run it;
• Keep tests fast: quick tests help you run them often and catch problems early.

By following these basic principles, you will build a strong foundation for testing your Spring Boot applications.