ci: fail legibly on missing Pages source, document both test files

Author: muhammetsafak

.github/workflows/deploy.yml

@@ -32,6 +32,8 @@ jobs:
       # Parity tests read dist/index.html, so they must run after the build.
       - run: npm test
 
+      - uses: actions/configure-pages@v5
+
       - uses: actions/upload-pages-artifact@v3
         with:
           path: ./dist

README.md

@@ -12,12 +12,19 @@ npm run dev
 ## Test
 
 ```sh
+npm run build   # tests/parity.test.mjs reads dist/index.html
 npm test
 ```
 
-The suite compares the built `dist/index.html` against `tests/fixtures/baseline.html`,
-a frozen copy of the pre-Astro page, and fails on any change to the page's metadata,
-links, headings or rendered text. Run `npm run build` first.
+The suite has two parts:
+
+- `tests/parity.test.mjs` compares the built `dist/index.html` against
+  `tests/fixtures/baseline.html`, a frozen copy of the pre-Astro page, and fails on any
+  change to its title, meta tags, canonical/favicon, JSON-LD, headings, anchors, images
+  or rendered body text.
+- `tests/data.test.mjs` checks `src/data/*.ts` directly, independently of the build —
+  entry counts, required fields and their types, Iconify icon id format, that every
+  repo URL is on github.com, and uniqueness of library names and repos.
 
 ## Deploy