edentext/docs/headless-testing.md

Headless browser testing

With no test suite, the way to verify rendering, layout, or interaction is to drive the live app in a headless browser. This container is linux arm64 (uname -m → aarch64) — the one gotcha. Use it for any check: pagination, list-marker/float layout, table sizing, header/footer, theme colors, image drag/resize, ODF round-trips, etc. PDF export is just one example.

• Don't use puppeteer / npx @puppeteer/browsers install chrome-headless-shell: they fetch an x86-64 Chrome that can't run here (rosetta error: failed to open elf at /lib64/ld-linux-x86-64.so.2). No arm64 chrome-headless-shell build exists.
• Use Playwright's Chromium (native arm64): npm install --no-save playwright-core && npx playwright-core install chromium → binary at ~/.cache/ms-playwright/chromium-*/chrome-linux/chrome. Playwright's install-deps host check errors out, but the libs install via apt: apt-get install -y libdbus-1-3 libnss3 libnspr4 libatk1.0-0 libatk-bridge2.0-0 libcups2 libdrm2 libxkbcommon0 libxcomposite1 libxdamage1 libxfixes3 libxrandr2 libgbm1 libasound2 libatspi2.0-0 libpango-1.0-0 libcairo2. Launch with playwright-core, executablePath at that binary, args: ['--no-sandbox'].

Then load npm run dev, inject a document into localStorage['edentext-doc'], reload, and read live DOM geometry (getBoundingClientRect, Range.getClientRects) or screenshot. This is the only way to exercise the editor's live ProseMirror NodeViews (e.g. the image node), which generateHTML can't reproduce. The debug/pagebreak-debug-*.json snapshots carry the live doc JSON, handy to inject.

For PDF-export repros specifically: replicate pdf.ts's clone + html2canvas(...) inside page.evaluate and read the canvas back as a PNG — capturing the real jsPDF doc.save() download tends to hang in headless. Inspect output PDFs with poppler-utils (apt-get install -y poppler-utils: pdftoppm, pdfimages, pdftotext).

Hunting for bugs the suite cannot see

npm run test:coverage says where to look: the logic modules are dense with tests, src/lib/components/** and App.svelte are at 0% — every bug found this way so far lived there. Give each probe a pageerror + console.error collector; that alone reports faults nobody predicted (two of six were found by clicking controls and reading the console).

Four passes, cheapest first:

1. Edges — junk in every edentext-* key, truncated/renamed/empty archives, a full localStorage, no IndexedDB, page-tall images, 400-section documents.
2. Breadth — click every control of every tab, watch only for uncaught errors.
3. Semantics — not "does it crash" but "is the answer right": reject a tracked change and compare against the original, TOC page numbers against the measured page of each heading, a numeric sort against 3/10/25. The worst bug found (a reject that ate the original text) crashes nothing.
4. Invariants — snapshot → act → undo → compare; page count stable over reloads; save → reopen; .docx and .odt of one corpus fixture giving identical counts.

Then repro minimally and take a stack trace off the dev server (sourcemaps) with Error.stackTraceLimit = 300 — the default ten frames stop above the cause.

Budget for false alarms. Three of four striking signals were the probe's own fault: Range.getClientRects also returns container rects (a layout checker built on it is noise), a stale button index reads as a dead control, and clicking .tiptap > p by index hits a different block once an edit has reflowed the document. Reproduce deterministically before touching any code.