new·The score now tells you which way it movedA brain's exam only ever grows: its own material writes questions, and so does every question a real caller asked and did not get answered. The score is a percentage over that growing set, so a brain that learned more could post a smaller number — and this week three did. One of them answered two MORE questions than the week before and showed eighteen points less. Printed as a single percentage, that reads as decline to a reader and as punishment to anyone who contributes material.all news →
mozg.beta
Sign in

explore / Web & frontend / mozg / Vitest

Vitest · API reference

Answer questions about the Vitest API exactly as specified: describe, test, expect and the vi object with every method's signature, and every assertion matcher with its behaviour.

1,081 notes · updated 2026-08-14 · trained 86%

since last sitting: +39 newly passed — this brain is learning · the verified changelog →

use this brain
# sign in to get a token
$ claude mcp add --transport http mozg \
https://mozg.sh/mcp --header "Authorization: Bearer …"
> use mozg/vitest-api — …
Sign in — get this command with your token in it

New here? Sign in and this exact command appears with your token already inside — copy, paste into your terminal, done.

Or just add it

Sign in and add it, and every agent you have connected can read it — nothing to download, and it stays current as the author updates it.

Sign in to add it

Ask it things like

answers 39/43 on its latest exam
What hooks are available and when do beforeAll, beforeEach, afterAll, afterEach run?hooks✓
Can you describe.skip, describe.only, and describe.todo - what do each do?describe API✓
What is the difference between toEqual and toStrictEqual?expect matchers✓
What does toThrow matcher do and what is required?expect matchers✓
What is test.each and how do you pass data - array vs object syntax?test API✓
What does vi.fn() do and what signature does it have?vi object✓
What does vi.spyOn do and what is required for class methods?vi object✓
What is vi.mock and what is its hoisting behavior?vi object✓

What it can answer

43 coverage checks
86%
Answers 39 of the exam's 43 questionsIt answers 39 questions, 39 more than last time, out of an exam that grew by 43.Nothing it used to answer has stopped working.
✓vi object15 / 15
▲expect matchers8 / 9
✓async and timing4 / 4
✓expect utilities4 / 4
▲DOM matchers2 / 3
✓hooks2 / 2
▲test API2 / 3
✓advanced mocking1 / 1
▲describe API1 / 2
exam badge — share this score →

Attacks survived

re-run weekly · 2026-08-10
✓gate-battery12/12 known hostile payloads caught by the ingest gate
✓injection-corpusevery active note scanned — no steering language
✓secret-corpusevery active note scanned — no keys or credentials

heuristic scans against known attack classes — measured and dated, not a promise of unpoisonability

Inside

  • vi.isWhenChain - type guard for When chains · vi object/methods
  • vi.mock - default export caveat · vi object/methods
  • vi.when - times option · vi object/methods
  • toHaveBeenExhausted assertion · expect api
  • vi.mock - spy option · vi object/methods
  • vi.mock - module promise signature · vi object/methods
  • vi.when - per-argument spy behavior · vi object/methods
  • vi.when - available then* methods · vi object/methods
  • vi.when example with fallback and times · vi object/methods
  • vi.when basic example · vi object/methods
  • vi.mock - function signature · vi object/methods
  • vi.mock - hoisting behavior · vi object/methods
  • vi.mock spy example · vi object/methods
  • vi.mock - __mocks__ folder support · vi object/methods

Licence

CC BY-NC-SA 4.0

Use it, copy it, build on it, with credit. Selling it is not allowed.