Parallel Resource Isolation

PORT=<free_port> next dev

Playwright with webServer config:

• Override port via env var, pass same port as baseURL
• If env-based port override isn't supported, flag the user — do NOT modify config files

Playwright without webServer (external server):

• Start dev server on the free port
• Run Playwright with overridden baseURL:

BASE_URL=http://localhost:<free_port> npx playwright test

Hardcoded baseURL in Playwright config (common case): Most configs hardcode baseURL: 'http://localhost:3000' instead of reading from env. If so, BASE_URL=... won't work. Flag the user with this exact fix:

Your playwright.config.ts has a hardcoded baseURL. Please update it to: baseURL: process.env.BASE_URL || 'http://localhost:3000' This lets me override the port via env var without modifying config files.

Database Isolation (Supabase)

Before running tests that write to or assert against the DB:

1. Determine if isolation is needed:
   • Reading only → share the DB, skip isolation
   • Writing / mutating / asserting on DB state → isolate
2. Generate a timestamp-based schema prefix: parallel_<epoch>_ (e.g., parallel_1741234567_)
3. Create the isolated schema and run migrations:

psql "$DATABASE_URL" -c "CREATE SCHEMA parallel_1741234567_;"
PGOPTIONS="--search_path=parallel_1741234567_" npx supabase db push

4. Point the app at the isolated schema via env var:

SUPABASE_SCHEMA=parallel_1741234567_ npx playwright test

5. After tests complete: drop the schema:

psql "$DATABASE_URL" -c "DROP SCHEMA parallel_1741234567_ CASCADE;"

Playwright Browser Isolation

Before running Playwright tests:

1. Check for running Playwright browser processes that could conflict
2. Isolate browser state to avoid lock contention — use either approach:

TMPDIR=/tmp/playwright_<epoch> npx playwright test

Or more targeted — isolate only the browser path:

PLAYWRIGHT_BROWSERS_PATH=/tmp/pw_browsers_<epoch> npx playwright install chromium
PLAYWRIGHT_BROWSERS_PATH=/tmp/pw_browsers_<epoch> npx playwright test

3. Ensure the Playwright instance targets the same port assigned in Port Isolation above

Reporting

After adapting, report once and move on:

⚡ Parallel isolation:
  Dev server: port 3005 (3000 was in use)
  DB schema: parallel_1741234567_
  Playwright: /tmp/playwright_1741234567

Only report resources that were actually adapted. If nothing conflicted, say nothing.

Quick Reference

Common Mistakes

Killing the other Claude's process

• Problem: Port 3000 is in use, so you kill the process to free it
• Fix: Never kill processes you didn't start. Pick a different port.

Modifying config files for port overrides

• Problem: Editing playwright.config.ts or next.config.js creates git conflicts
• Fix: Use environment variables. If env vars don't work, flag the user.

Forgetting to pass the adapted port to Playwright

• Problem: Dev server on 3005, Playwright still hits 3000
• Fix: Always coordinate — the port assigned to the dev server must be passed as BASE_URL to Playwright.

Isolating the DB when not needed

• Problem: Overhead of schema creation for read-only tests
• Fix: Only isolate when tests write or assert on DB state.

Red Flags

Never:

• Kill another process to free a resource
• Modify config files to change ports
• Ignore port conflicts and hope for the best
• Skip DB cleanup after tests

Always:

• Check before starting
• Adapt silently via env vars
• Report what you chose
• Clean up DB schemas after tests