@houserules/plugin-testing

An agent asked to fix a bug will often write a test that passes before the fix and after it, which proves nothing. Left alone, it also drifts toward asserting toBeDefined(), chasing a coverage number, or filing a test by the directory it sits in rather than by what it doubles.

This plugin ships a testing discipline rule that does not assume a framework. It covers whether a test is worth writing, where it lives, what it should assert, and how it is named, for any runner with a describe/it shape, plus opt-in guides for the languages that need suffix and build-exclusion detail the base rule leaves out.

Install

pnpm add -D @houserules/plugin-testing
pnpm exec houserules init

Requires @houserules/cli. init is what writes the module into .claude/. This module is off by default, so select it when init asks.

Modules

• testing installs .claude/rules/testing.md, a path-scoped rule matched to *.test.ts, *.test.tsx, *.test.mts, *.test.js, *.test.mjs, and the .spec.* equivalents. It covers whether a test earns its place (it has to fail when the behavior it covers breaks), where tests colocate (one test directory beside the subject, __tests__/ by default), what to test and at what level, Arrange/Act/Assert structure, and naming that states the observable behavior rather than the implementation. init can also record the repo's test-directory name (__test__ or tests) as a module option, so the layout checker (test-layout.mjs --test-dir <name>) judges against it instead of the default.

  init also prompts for language guides to install alongside it. Five exist today. TypeScript (testing-typescript) and JavaScript (testing-javascript) are each installed as their own path-scoped rule with the concrete suffix list, runnable examples, and build-exclusion advice the base rule leaves to them. Svelte (testing-svelte) covers runner setup for testing Svelte 5 components and .svelte.ts reactive modules. 3D and WebGL (testing-3d) is domain guidance for tests that cover Three.js scenes and other WebGL code. Simulation (testing-simulation) is domain guidance for tick loops, seeded randomness, and floating arithmetic. TypeScript is selected by default.

  Because the rule is path-scoped, Claude Code loads it only when a matching test file is in the working set, so it costs nothing on the always-loaded surface.

• playwright-mcp installs the Playwright MCP server config under .claude/mcp/, as playwright.stdio.json and playwright.vscode.json. houserules never writes .mcp.json, so an advise action explains how to wire one of them into this repo's own config. Reach for it for cross-browser work and test assertions. For performance traces, Lighthouse, and heap snapshots, chrome-devtools-mcp in @houserules/plugin-design is the pick, and the advise text in both modules says so.

  The default surface is 24 tool definitions, paid on every turn whether you use them or not, and the shipped --caps=testing brings it to 29. Every other capability is opt-in through --caps. The args pin @playwright/[email protected], because the package is pre-1.0 and @latest could change the tool surface without warning, and they carry --headless and --isolated. Switching browsers is a one-word edit: --browser firefox, --browser webkit, or --browser msedge.

Upgrading from the CLI core

testing was a built-in CLI module. A repo that recorded it before the split gets a HouseError on its next init or update naming this package. Installing it and adding it to the plugins array in .claude/houserules.config.json restores the module and its files. Nothing is deleted in the meantime.

Part of houserules

houserules is a portable set of Claude Code infrastructure that keeps the agent's context lean. This is one of twelve first-party plugins. The package list has the rest.

License

MIT. See LICENSE.