Unit testing

Unit testing is a type of software testing that focuses on verifying the smallest testable parts of a program, called units, to ensure they work as intended. A unit can be a single function, method, or module in the codebase. Unit tests are typically automated and written by developers during or after coding to validate specific logic and catch errors early.
The primary goal of unit testing is to confirm that each unit performs correctly in isolation before integrating it with other components. This approach reduces bugs, simplifies debugging, and improves software reliability.
Advanced
Unit testing is usually carried out with frameworks such as JUnit for Java, pytest for Python, NUnit for .NET, or Jasmine for JavaScript. Tests are often written alongside production code, supporting development practices like Test-Driven Development (TDD). Mocking and stubbing are used to simulate dependencies, ensuring that tests evaluate only the specific unit in question.
Advanced unit testing strategies focus on code coverage, regression prevention, and integration into CI/CD pipelines. Effective unit tests are automated, repeatable, independent, and fast. When combined with integration and system testing, they contribute to a layered quality assurance process.
Relevance
Applications
Metrics
Issues
Example
A financial app developer wrote unit tests for interest calculation functions. During testing, a bug was detected in edge cases with leap years. Fixing this early prevented costly errors in production, improved reliability, and boosted user trust in the app.