Test behavior, not implementation — test what code does, not how
For behavior changes, write the failing test first and verify it fails for the expected reason
Follow the testing pyramid — more unit tests, fewer E2E
Use meaningful coverage metrics — branch coverage over line coverage
Prevent flaky tests — no arbitrary waits, no test interdependence

When NOT to Use

For TDD discipline during implementation — see work-session anti-rationalization reference
For security testing — see security-audit skill

Quick Start Checklist

Choose test framework (Vitest recommended for new projects)
Design test folder structure mirroring source
Write unit tests for pure logic and utilities
Add integration tests for API endpoints and data flows
Add contract tests against OpenAPI spec (if applicable)
Add E2E tests for critical user journeys only
Set up CI to run tests on every PR
Before completion claims, run verification-before-completion and cite the fresh command result

What NOT to Test

Framework internals (React rendering, Express routing)
Third-party library behavior
Trivial getters/setters with no logic
Implementation details (private methods, internal state)

References

Reference	Description
test-architecture-structure.md	Project structures, shared utilities, test configuration
test-architecture-isolation.md	Playwright config, database isolation, performance optimization
test-design-techniques.md	Equivalence partitioning, boundary values, decision tables, state transitions
test-design-error-and-advanced.md	Error handling tests, property-based testing, parameterization, regression
frontend-react-testing.md	React Testing Library, queries, user events, hooks, forms
frontend-vue-a11y-visual.md	Vue Test Utils, accessibility, visual/Storybook testing, anti-patterns
e2e-playwright.md	Playwright POM, fixtures, auth state, API mocking, visual comparison
e2e-cypress-and-stability.md	Cypress patterns, flaky test prevention, test data, debugging
mocking-fundamentals.md	Mock decision tree, stubs/mocks/spies/fakes, MSW setup and usage
mocking-modules-and-patterns.md	Module mocking, time mocking, anti-patterns, dependency injection
coverage-guide.md	Coverage metrics, meaningful thresholds, CI integration
api-test-frameworks-setup.md	Vitest and Jest setup, configuration, running tests
api-test-supertest-and-helpers.md	Supertest usage, request helpers, custom matchers, snapshots, debugging
api-integration-patterns.md	CRUD endpoint tests, relationship tests
api-auth-patterns.md	Login/logout, protected routes, authorization, auth helpers
api-e2e-and-edge-cases.md	Multi-step workflow tests, error responses, edge cases
api-test-data-factories.md	Factory patterns, builders, fixtures
api-test-data-database.md	Database helpers, cleanup strategies, data generation
api-contract-openapi.md	OpenAPI/AJV schema validation, contract tests
api-contract-zod-advanced.md	Zod validation, response shape testing, breaking change detection
api-test-ci-pipelines.md	CI pipeline strategy, GitHub Actions, parallel execution
api-test-ci-environments.md	Environment config, test reporting, database services, E2E environments
anti-rationalization.md	Iron Law, common rationalizations, red flag STOP list for TDD discipline

Runtime Notes

Claude Code: dispatch yokay-test-runner via the Task tool with subagent_type: "pokayokay:yokay-test-runner".
Codex: there is no subagent dispatch. Execute the agent's role inline — read the corresponding agents/yokay-<name>.md and follow its Behavioral Defaults, Critical Rules, and Output Contract directly in the current session.

Level	Speed	Cost	Confidence	Share
Unit	~1ms	Low	Narrow	65-80%
Integration	~100ms	Medium	Medium	15-25%
Contract	~10ms	Low	API shape	Part of unit
E2E	~1s+	High	Broad	5-10%

testing-strategy

Testing Strategy

Test Pyramid

Key Principles