Vitest in Core

Use the repository harness as the source of truth. Core currently resolves Vitest 5.0.3 from bun.lock; verify the exact version before relying on a newly introduced API.

Authority and test surface

Read these before changing tests or configuration:

• vitest.config.ts — include globs, aliases, Node default environment, timeouts, mock clearing, setup, and the custom coverage provider.
• tests/setup/unit-env.ts — safe env defaults and browser shims.
• scripts/verify/unit-tests.mjs — the full unit gate and platform behavior.
• docs/ai/rules/testing.md — repository-wide test and CI policy.
• .next-docs/01-app/02-guides/testing/vitest.mdx when testing Next.js code.

Do not use bun test; that selects Bun's test runner. Use Vitest through the committed scripts or bunx vitest.

Commands

# Full CI-equivalent unit suite with Core's coverage provider
bun run test:unit

# Focused file or directory while iterating
bunx vitest run tests/unit/path/to/example.test.ts

# Focused test name
bunx vitest run tests/unit/path/to/example.test.ts -t "expected behavior"

# Watch a focused surface
bunx vitest tests/unit/path/to/example.test.ts

# Structured failure report and targeted reruns
bun run test:unit:feedback

Workflow

1. Choose the boundary. Test observable behavior at the smallest stable public boundary. Prefer pure logic/unit coverage; use Playwright when the claim depends on a real browser, routing, hydration, or an async Server Component.
2. Place the test in an included path. Match the existing tests/unit, packages/api/tests/unit, or packages/auth conventions from vitest.config.ts; do not invent a disconnected test root.
3. Control the environment. The default is node. Add // @vitest-environment jsdom only to files that need DOM APIs, and clean up rendered components and mutated globals.
4. Mock boundaries, not the unit's internals. Remember that vi.mock is hoisted. Use vi.hoisted for shared mock state, dynamic imports when a module must load after mocks, and vi.importActual for intentional partial mocks.
5. Reset all changed state. clearMocks: true clears call history but does not restore globals, timers, dates, env values, or spy implementations. Undo those changes in hooks.
6. Run focused, then full. Iterate on the smallest file/name filter and run bun run test:unit before handoff.

Core-specific guardrails

• Unit tests must not call live Supabase, Stripe, Resend, Payload, or network services. Use deterministic fakes at repository boundaries.
• Keep real credentials out of tests. The committed env defaults are placeholders and intentionally clear the Supabase service-role key.
• Assert behavior and durable contracts, not incidental class strings or implementation order unless that order is itself the contract.
• Prefer explicit test data builders/helpers over large untyped fixture blobs.
• Avoid .only; use .skip/.todo only with a documented reason and no hidden loss of required coverage.
• Core's custom raw V8 coverage provider records script/function information but does not compute line, statement, or branch coverage. Its placeholder totals do not establish coverage quality. Do not claim a threshold the provider does not measure.

Checklist

• The test exercises an observable contract at the right test layer.
• The file is inside a configured include path and uses the correct env.
• Mocks intercept external boundaries and respect Vitest hoisting.
• Globals, env, timers, dates, spies, DOM, and module state are isolated.
• Assertions are deterministic and do not depend on network or test order.
• Focused tests pass, then bun run test:unit passes.
• Coverage output is described without overstating its current signal.

Provenance

See references/upstream.md for the reviewed upstream source, version compatibility decision, license, and refresh workflow.