testing

name	testing
description	Skill: testing
metadata	{"skiller":{"source":".agents/rules/testing.mdc"}}

Testing Goal

Keep tests in three buckets only:

• Pure unit tests for deterministic logic.
• Thin component or hook contract tests for real app behavior.
• Golden input or output tests when serialized output is the contract.

Hard constraints:

• Prefer Bun for the fast local loop.
• Keep the default suite fast.
• No browser or e2e coverage unless the app behavior truly needs it.
• Coverage is a hotspot tool, not a vanity score.

Core Rules

• Assert public behavior, not implementation detail.
• Keep tests next to the code they cover with *.spec.ts[x].
• Keep helpers local. Do not import one spec from another.
• Prefer explicit assertions over snapshots.
• Delete skipped, commented, or placeholder tests instead of babysitting them.

Seam Selection

• Use plain function tests for pure logic.
• Use rendered React tests for hooks, components, rerender behavior, and DOM behavior.
• Use browser checks only when the contract is actually browser-specific.

Fixtures And Assertions

• Keep fixtures small.
• Use plain objects for simple state.
• Use it.each for small behavior matrices.
• In Bun + Testing Library, prefer render-returned queries over screen.
• Use direct style-property assertions instead of toHaveStyle.
• Use snapshots only when serialized output is the contract and inline assertions would be worse.

Quick Reference

• Keep tests fast and local.
• Start with the smallest seam that proves the behavior.
• Prefer explicit assertions.
• Browser checks are for real UI behavior, not lazy coverage.