Unit Testing
Unit Testing verifies that individual pieces of code work correctly in isolation – before they interact with the rest of the system.
What Is Unit Testing?
Unit Testing is the practice of writing and running automated tests for individual units of code – such as functions or classes – to verify they behave correctly in isolation. Unit tests execute a specific code path with defined inputs and assert that the output matches the expected result, providing fast, targeted feedback on whether a change has introduced a regression.
Unit tests are the foundation of an automated test suite. They are fast to run, easy to isolate, and directly tied to specific code behaviour – making them the most immediate feedback mechanism available when a developer makes a change. A failing unit test identifies exactly which function is broken and what output was expected versus received.
Writing good unit tests requires discipline: tests should be independent of each other, deterministic in their outcomes, and focused on a single behaviour rather than testing multiple things at once. Tests that depend on external systems, produce different results on different runs, or test too many things simultaneously become unreliable – contributing to the flakiness that erodes confidence in the test suite.
AI tools are increasingly used to generate unit tests for existing code that lacks coverage – analysing the structure and logic of a function to produce tests that exercise its key behaviours and edge cases. This reduces the effort required to reach meaningful coverage thresholds and helps teams maintain coverage as the codebase grows.
