javascript-typescript-jest SKILL.md skillA
javascript-typescript-jest from marielynneblock/arcanum-artifex is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add marielynneblock/arcanum-artifex/javascript-typescript-jest@git:20260710.0115f49Pins git:20260710.0115f49 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- marielynneblock/arcanum-artifex
- Path
skills/development/typescript/javascript-typescript-jest/SKILL.md- Versions recorded
- 4
- Latest version
- git:20260710.0115f49, committed Jul 10, 2026
- First version recorded
- May 10, 2026
- Size
- 2,284 bytes
- Repository stars
- 4
- License
- none declared
Best practices for writing JavaScript/TypeScript tests using Jest, including mocking strategies, test structure, and common patterns.
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
### Test Structure
- Name test files with `.test.ts` or `.test.js` suffix
- Place test files next to the code they test or in a dedicated `__tests__` directory
- Use descriptive test names that explain the expected behaviour
- Use nested describe blocks to organise related tests
- Follow the pattern: `describe('Component/Function/Class', () => { it('should do something', () => {}) })`
### Effective Mocking
- Mock external dependencies (APIs, databases, etc.) to isolate your tests
- Use `jest.mock()` for module-level mocks
- Use `jest.spyOn()` for specific function mocks
- Use `mockImplementation()` or `mockReturnValue()` to define mock behaviour
- Reset mocks between tests with `jest.resetAllMocks()` in `afterEach`
### Testing Async Code
- Always return promises or use async/await syntax in tests
- Use `resolves`/`rejects` matchers for promises
- Set appropriate timeouts for slow tests with `jest.setTimeout()`
### Snapshot Testing
- Use snapshot tests for UI components or complex objects that change infrequently
- Keep snapshots small and focused
- Review snapshot changes carefully before committing
### Testing React Components
…Read the whole file at its exact version.
How to install
mdr add marielynneblock/arcanum-artifex/javascript-typescript-jest@sha256:b374f73d5e9306e6The line at the top of this page pins the label git:20260710.0115f49, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_45a2pbb6jvwnchya)
4 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 4 versions of this file, between May 10, 2026 and Jul 10, 2026, about one every 20 days.
| version | committed | commit | size | audit | |
|---|---|---|---|---|---|
| git:20260710.0115f49 latest | 2026-07-10 | 0115f49 | 2,284 B | A | view · diff |
| git:20260710.ffb3400 | 2026-07-10 | ffb3400 | 2,281 B | A | view · diff |
| git:20260515.b861afb | 2026-05-15 | b861afb | 2,281 B | A | view · diff |
| git:20260510.f26bcec | 2026-05-10 | f26bcec | 2,235 B | A | view |
Audit of the latest version
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (2284 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No curl or wget piped into a shell
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Source
marielynneblock/arcanum-artifex · 4 stars · license none declared · pushed 2026-09-19 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_45a2pbb6jvwnchya GET https://markdownregistry.com/api/v1/resolve?ref=marielynneblock/arcanum-artifex/javascript-typescript-jest GET https://markdownregistry.com/api/v1/blob/b374f73d5e9306e63fc159c3657f0fbbda2ee5d7134da081dd97c61e289c9964
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.