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Playwright table proof can reuse a stale existing server

docs/solutions/test-failures/2026-05-23-playwright-reuses-stale-existing-server.md

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Playwright table proof can reuse a stale existing server

Problem

Slate v2 Playwright tests default to reuseExistingServer locally. If a server is already running on the configured port, tests can exercise stale built output instead of the source just edited.

Symptoms

  • A table test expected the new trailing paragraph length, but the page returned the old paragraph text.
  • Selection assertions failed with a shorter offset from the stale page.
  • Drag-selection assertions saw the old example copy even after the source and test were patched.

What Didn't Work

  • Rerunning the same Playwright command kept hitting the existing server.
  • Hardcoding the example paragraph in the test made the stale-server mismatch worse because the test and page could drift.

Solution

For source edits that affect rendered examples, build the static site and run Playwright against a fresh server on a separate port:

bash
cd .tmp/slate-v2
bun build:next
PORT=3111 bun serve:playwright
PLAYWRIGHT_BASE_URL=http://localhost:3111 PLAYWRIGHT_RETRIES=0 \
  bunx playwright test playwright/integration/examples/tables.test.ts \
  --project=chromium --workers=1

When a test needs the current example text, derive it from the rendered page:

ts
const trailingParagraph =
  (await editor.root.locator('p').last().textContent()) ?? ''

Why This Works

PLAYWRIGHT_BASE_URL disables the Playwright config's managed web server and points tests at the fresh server. Using a separate port avoids killing the developer server the user may be using. Deriving text from the page prevents source/test string duplication from becoming a false failure.

Prevention

  • After changing example text or static route content, do not trust a local reused Playwright server.
  • Use a one-off static server on a separate port for final proof when the dev server must stay running.
  • Prefer page-derived text in browser tests when the exact text is not the behavior under test.