What is Test data isolation in Laravel, and what role does it play in a real application?

What is Test data isolation in Laravel, and what role does it play in a real application? In Laravel, test data isolation should be understood as part of a larger application architecture rather than as an isolated API call. Factories are commonly combined with transactional or resettable test database strategies so tests do not depend on existing data. A strong understanding includes its purpose, the layer where it belongs, the data or request flow it affects, and the situations where another mechanism may be more appropriate. Practical context: Seeders provide intentional data-loading workflows while model factories generate realistic model records for development and testing. The specific focus here is test data isolation: Factories are commonly combined with transactional or resettable test database strategies so tests do not depend on existing data. This question is designed to test not only terminology, but also how the concept fits into Laravel's request, application, database, security, or deployment workflow.