Software unit testing is a technique that focuses on individual components or units of an application in isolation from the rest of the application, verifying their functionality and intention. Effective unit tests should be modular, self-contained, repeatable, focused on a specific aspect of the code, fast, repeatable and deterministic, simple and readable, test for all scenarios, maintainable, and tested continuously. There are several common mistakes to avoid when writing unit tests, including depending on external services, over-dependence on code coverage metrics, dependence on implementation details, testing multiple things at a time, writing tests after the fact, not updating tests when code changes, not testing for error conditions, and not using enough assert statements. To improve or start unit testing, various tools are available for different programming languages, such as Pytest, Behave, Doctest, Robot Framework, Unittest, Coverage, Tox, Nose2, AVA framework, Jasmine, Mocha, Jest, Testing Library, TestDouble, Chai, Karma, Sinon, Istanbul, Gauge Framework, CodiumAI, and Selenium for cross-platform tools.