A Deep Dive into Unit Testing

A software product encompasses more than just business code, incorporating elements such as documentation, CI/CD pipelines, communication rules, and automated tests, all integrated into a cohesive system. In modern software development, testing has become foundational, guiding architecture design and ensuring code testability, with unit tests forming just one part of a broader testing strategy. Unit testing involves writing tests for isolated pieces of functionality, or "units," and is central to test-driven development (TDD), a methodology where tests are written before the business code. The article discusses two schools of TDD: the Detroit School, which uses real classes or stubs for testing, and the London School, which prefers mocks for isolating dependencies. It further emphasizes best practices for writing effective unit tests, such as not violating the dependency inversion principle, ensuring tests are deterministic, fast, and environment-independent, and running all tests in a CI environment to prevent broken code from being merged. Additionally, it highlights the importance of naming conventions, meaningful error messages, and proper test data initialization for maintainability, as well as the tools available for unit testing in Java, like JUnit, Mockito, and Spock.