docs: add design spec for eslint-config and prettier-config test suite

.github/workflows/test.yml

@@ -0,0 +1,30 @@
+name: Test
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 24
+          cache: 'pnpm'
+          registry-url: 'https://npm.pkg.github.com'
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+        env:
+          NODE_AUTH_TOKEN: ${{secrets.GITHUB_TOKEN}}
+
+      - name: Run tests
+        run: pnpm test

.husky/pre-push

@@ -0,0 +1 @@
+pnpm test

README.md

@@ -36,10 +36,25 @@ pnpm dep:outdated  # Check for outdated dependencies across workspaces
 pnpm dep:update    # Update all dependencies
 ```
 
+## 📝 Testing
+
+```bash
+pnpm test
+```
+
+Added to catch two types of problems:
+- **Dependency updates** silently changing rules
+- **Our own config edits** disabling or weakening rules
+
+Each package has two test files:
+- `config.snapshot.test.js` — snapshots the full config and fails on a change
+- `rules.test.js` / `format.test.js` — behavioral tests that lint/format real code snippets
+
+Tests run on pre-push and in GitHub Actions on every pull request.
+
 ## 🎨 Formatting & Linting
 
-The linting in this monorepo uses the settings defined in the child packages.
-Husky (CaptainHook alternative) ensures that all files are automatically formatted and linted with each commit.
+The linting in this monorepo uses the settings defined in the child packages. Husky ensures that all files are automatically formatted and linted with each commit.
 
 ## About us
 

package.json

@@ -9,8 +9,12 @@
 	},
 	"license": "EUPL-1.2",
 	"private": true,
+	"publishConfig": {
+		"registry": "https://npm.pkg.github.com/@yardinternet"
+	},
 	"packageManager": "pnpm@10.33.0",
 	"scripts": {
+		"test": "vitest run",
 		"lint:js": "yard-toolkit lint js -m custom ./packages/**/src/**/*.js",
 		"format:js": "yard-toolkit format js -m custom ./packages/**/*.js",
 		"dep:check": "syncpack list-mismatches",
@@ -21,9 +25,13 @@
 	},
 	"type": "commonjs",
 	"devDependencies": {
+		"@babel/core": "^7.29.7",
+		"@babel/eslint-parser": "^7.25.7",
+		"@yardinternet/toolkit": "workspace:*",
 		"husky": "^9.1.7",
 		"lerna": "^9.0.4",
 		"lint-staged": "^16.2.7",
-		"syncpack": "^14.0.0"
+		"syncpack": "^14.0.0",
+		"vitest": "^3.2.6"
 	}
 }

packages/eslint-config/package.json

@@ -4,7 +4,7 @@
 	"description": "Eslint configuration",
 	"main": "src/index.js",
 	"scripts": {
-		"test": "echo \"Error: no test specified\" && exit 1"
+		"test": "vitest run"
 	},
 	"publishConfig": {
 		"registry": "https://npm.pkg.github.com/"
@@ -18,6 +18,7 @@
 	"author": "",
 	"license": "ISC",
 	"dependencies": {
+		"@babel/eslint-parser": "^7.25.7",
 		"@babel/preset-react": "^7.29.7",
 		"@eslint/compat": "^2.1.0",
 		"@eslint/eslintrc": "^3.3.3",
@@ -29,5 +30,9 @@
 		"eslint-plugin-import": "^2.32.0",
 		"eslint-plugin-react-hooks": "^7.1.1",
 		"globals": "^17.6.0"
+	},
+	"devDependencies": {
+		"eslint": "^9.39.4",
+		"vitest": "^3.2.6"
 	}
 }