Unit tests exercise a small piece of PHP code in isolation and generally do not boot the full Laravel application. They are fast and useful for pure business rules, value objects, and focused service behavior.

Feature tests boot Laravel and test an application behavior across layers, such as an HTTP request, authentication, validation, database state, queue dispatch, or response. Browser tests drive a real browser through user-visible behavior and are slower but valuable for JavaScript interactions and complete critical journeys. Use the smallest test level that gives confidence.