Test patterns

Apply the runner-specific reference matching the detected test runner. Principles apply to all stacks.

Reference files

References

• Vitest: https://vitest.dev/
• Jest: https://jestjs.io/
• React Testing Library: https://testing-library.com/docs/react-testing-library/intro/
• Testing Library guiding principles: https://testing-library.com/docs/guiding-principles/
• Playwright: https://playwright.dev/
• pytest: https://docs.pytest.org/en/stable/
• pytest-django: https://pytest-django.readthedocs.io/
• Kent C. Dodds (Testing Trophy): https://kentcdodds.com/blog/the-testing-trophy-and-testing-classifications
• Martin Fowler (Test Pyramid): https://martinfowler.com/articles/practical-test-pyramid.html
• MSW: https://mswjs.io/
• fast-check: https://github.com/dubzzz/fast-check
• hypothesis: https://hypothesis.readthedocs.io/en/latest/

Version notes

Checked: 2026-09-26 against https://pypi.org/project/pytest/ and the migration and release pages listed above

• Vitest 4.x (Context7 /vitest-dev/vitest); the migration guide at vitest.dev lists for the next major: vi.mock / vi.unmock / vi.hoisted must be module-scoped, clearMocks defaults to true, automocked modules return undefined in browser mode. None of the patterns in reference/vitest-and-jest.md depend on the old behavior.
• Jest 30 (2025-06): --testPathPattern renamed --testPathPatterns; expect aliases removed. pytest 9 (2025-11; 9.1.1 current): fixture visibility now decides precedence over registration order; PytestRemovedIn9Warning is an error.
• MSW 2: http / HttpResponse replace rest and the req, res, ctx signature. Unchanged.