Test Writer
Generates unit tests for a specific function or module with sensible edge cases — happy path, sad path, and 2-3 boundary cases.
Entry verified April 21, 2026
The short answer
The test-writing skill that bridges "I should add tests" and "I have tests". Takes a function, produces a test file covering the obvious paths plus a handful of edge cases. Not a replacement for thinking about tests — a replacement for the boilerplate around them.
When to use it
On pure functions (parsers, validators, formatters). On business-logic modules with clear inputs and outputs. Avoid for integration-heavy or UI-driven code where mocking cost exceeds the payoff.
Setup
- 1
Save the file as ~/.claude/commands/test-writer.md.
- 2
Skill reads the project's testing conventions — .claude/rules/testing.md if present, otherwise looks for a jest, vitest or mocha config.
- 3
Invoke: /test-writer path/to/module.js; skill writes the matching test file.
- 4
Verify the generated tests actually fail when the code is broken — otherwise you have tautological tests that pass regardless.
Example
You: /test-writer lib/claude-data.js Claude: Writing tests/claude-data.test.js with 8 test cases covering getModelById happy path, legacy lookup, null input, and tier filter.
Source & attribution
- Author
- Bryan Collins + community pattern
- Licence
- MIT
- Type
- Original
Original pattern published under MIT — attribution preserved by convention, not licence requirement.
Caveats
Verify the tests actually fail when the code is broken — skill can produce tautological tests if the implementation leaks into the assertion.
56 skills across 10 categories, all licence-verified.