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test/README.md

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+# Visual testing rig
+
+Dummy backend + frozen fixtures + screenshot reference/compare. No npm deps
+beyond the repo (uses system Chrome at `/usr/bin/google-chrome`).
+
+## Workflow
+
+```bash
+# Build reference screenshots from live data (:4208 must run in dashback).
+# Collects fixtures, then captures 21 routes × 2 viewports into
+# test/screenshots/reference/ (committed to git).
+npm run rig:reference
+
+# Capture fresh screenshots and compare against reference (all in one).
+# Fails when > 0.1% of pixels differ; diffs → test/screenshots/diff/
+npm run rig:compare
+```
+
+## Viewports
+
+- `1920x1200`, `1280x960` (see `test/routes.mjs`)
+
+## Files
+
+| File | Role |
+|---|---|
+| `test/routes.mjs` | Route + viewport definitions (concrete ids: `ART-000001`, delivery `6`, entity `1`) |
+| `test/collect.mjs` | Fixture collector (mints JWT via dashback env + signing lib) |
+| `test/dummyBackend.mjs` | Always-authed stub serving `test/fixtures/snapshot.json` + `images/` |
+| `test/cdp.mjs` | Zero-dep CDP client (fresh page target per shot, settle wait, PNG capture) |
+| `test/capture.mjs` | Orchestrates dummy + vite + Chrome |
+| `test/compare.mjs` | Zero-dep PNG decoder + comparator (0.1% tolerance, red diff PNGs) |
+| `test/fixtures/` | Committed snapshot + binary thumbs (2.5 MiB) |
+| `test/screenshots/reference/` | Committed reference PNGs (7.5 MiB) |
+
+## Notes
+
+- `vite.config.js` honors `RIG_API_TARGET` for the `/api` proxy (default `http://localhost:4208`),
+  so the rig runs alongside live dev servers on :4208/:4209.
+- The dummy holds `/api/events` open with heartbeats and never emits — fixtures stay frozen.
+- Mutations (POST/PATCH/PUT/DELETE) echo fixtures so UI actions don't crash mid-run.
+- `GET /api/history` and `GET /api/article/history` don't exist in the backend yet
+  (frontend already renders empty grids); the collector stores empty fixtures for them.
+- Capture waits for `#root` content > 20 KB with zero `[role=progressbar]` spinners,
+  plus a settle delay, then hides carets/scrollbars for determinism.