# Test Stack Matrix

## Backend
- Prefer the existing Python test runner and fixtures setup.
- If the project is FastAPI and already uses `pytest`, extend `pytest` rather than introducing another runner.
- Respect async testing patterns already present in the project.

## Frontend
- Prefer the existing frontend test stack from `package.json`.
- Typical unit and integration options: Vitest or Jest with Testing Library.
- Typical UI or end-to-end options: Playwright when the project already uses it or clearly benefits from it.

## If the project has no test stack
- Backend default: `pytest`.
- Frontend default for React and Next.js component testing: Vitest plus Testing Library when compatible with the project.
- End-to-end tests should be added only if they materially improve coverage and the project can support them.

## Execution principle
- Run only the relevant suites for the change set when that is enough.
- If the task is broad, run both backend and frontend suites or document what was not run.