Javascript Testing Expert

This one pushes you toward better testing practices in JavaScript, starting with tests as documentation before moving into edge case hunting with property-based testing via fast-check. It's opinionated about structure (AAA pattern, "should" naming, one describe per function) and actively warns you when code needs too many mocks to test, treating that as a code smell. The approach splits simple documenting tests from advanced property-based ones without explicit markers, just ordering. It's built for vitest and testing-library, advocates stubs over mocks, and wants you to avoid snapshot overuse and indeterministic tests. Good if you're tired of flaky test suites or want to find bugs you didn't think to write cases for.

skills.sh installs: 269
GitHub stars: 5.2K
last updated: Aug 21, 2026

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Install

$ npx -y skills add dubzzz/fast-check --skill javascript-testing-expert --agent claude-code

Installs into .claude/skills of the current project.

Files

⚠️ Scope: Testing functions and components, not black-box e2e.

🏅 Main objectives: use tests as a way to...

uncover hard to detect bugs
document how to use the code
avoid regressions
challenge the code

🔧 Recommended tooling: vitest, fast-check, @fast-check/vitest, @testing-library/*, @vitest/browser-playwright, msw installed as devDependencies.
✅ Do try to install missing and relevant tooling, only recommend for @fast-check/vitest and browser testing.
✅ Do highly recommend user to install missing and relevant tooling.
✅ Do adapt yourself to missing tools.

File and code layout

✅ Do mimic the existing test structure of the project when adding new tests

✅ Do use one test file per code file

👍 Prefer using .spec.ts extension (e.g., fileName.ts → fileName.spec.ts) and colocated with the source file if no existing test structure is present

✅ Do put it within describe, when using it

👍 Prefer it over test

✅ Do name the describe with the name of the function being tested

✅ Do use a dedicated describe for each function being tested

SKILL.md on GitHub

Details

Repository: github.com/dubzzz/fast-check
Categories: Testing & QA, Documentation, Code Review & Quality, Python
First seen: Jun 3, 2026