testing-craft — Claude Code skill: what it does, how to install
Organizes automated checks along a strict hierarchy from static types to end-to-end runs. Useful when reviewing test suites or choosing verification levels for new code.
npx skills add jssblck/agents --skill testing-craft -a claude-codeWhat testing-craft does
The skill assigns every system invariant to the earliest verification layer capable of handling it. Type systems and linters catch compile-time errors first, keeping unit test suites focused on pure calculations and parser logic. Heavier database interactions run against isolated instances like Postgres or temporary directories, while third-party service calls go through Vercel Emulate.
Mocks and fakes must satisfy strict interface definitions. Because untyped assertions hide contract drift, the skill forbids casts such as as any and refuses to mock the actual target under verification. Production designs should not bend merely to accommodate test setups.
Built-in references target Rust, TypeScript, Go, and Python. Once a stronger layer takes over an invariant, the superseded test is removed to prevent redundant execution.
What it helps with
- assign code invariants to compiler types before writing runtime tests
- eliminate redundant tests that repeat existing type or lint guarantees
- construct compiler-checked doubles without resorting to untyped casts
- isolate database queries and provider protocols with dedicated test harnesses
Example prompts for the agent
- Review our TypeScript parser tests using
testing-craft - Plan verification rungs for the new Go payment service with
testing-craft - Audit redundant database tests in our Rust repository
How to install testing-craft
1Skills CLI (Vercel)
npx skills add jssblck/agents --skill testing-craft -a claude-code2Manually: put the files in place
~/.claude/skills/testing-craft/SKILL.mdCopy the whole skill folder; for one project use .claude/skills/testing-craft/
1Skills CLI (Vercel)
npx skills add jssblck/agents --skill testing-craft -a codex2Manually: put the files in place
.agents/skills/testing-craft/SKILL.mdFor all projects use ~/.agents/skills/
1Skills CLI (Vercel)
npx skills add jssblck/agents --skill testing-craft -a cursor2Manually: put the files in place
.cursor/skills/testing-craft/SKILL.mdCursor also reads .agents/skills/ and .claude/skills/
1GitHub CLI
gh skill install jssblck/agents testing-craft2Manually: put the files in place
.github/skills/testing-craft/SKILL.md1Skills CLI (Vercel)
npx skills add jssblck/agents --skill testing-craft -a gemini-cli2Platform CLI
gemini skills install https://github.com/jssblck/agents --path skills/testing-craftManually: put the files in place
.devin/skills/testing-craft/SKILL.mdThe legacy .windsurf/skills/ path still works
Skills CLI (Vercel)
npx skills add jssblck/agents --skill testing-craft -a opencodeClaude.ai
Zip the folder and upload it in Settings → Capabilities → Skills
Step by step, with commands for each platform: How to install skills in Claude Code: five ways
Questions about testing-craft
How do I install testing-craft in Claude Code?
Run npx skills add jssblck/agents --skill testing-craft -a claude-code in your terminal. Alternatively, save the file to ~/.claude/skills/testing-craft/SKILL.md.
What is the main principle behind testing-craft?
It enforces a verification ladder where types and linters verify preconditions first, leaving unit and integration tests only for behavior that static checks cannot validate.
Which programming languages does testing-craft support?
The skill specifies guidance for Rust, TypeScript, Go, and Python.
