Lessons from a complete test suite rewrite — what we would do differently

We rewrote our entire test suite (600 tests → 800 tests, Selenium Java → Playwright TypeScript) over 8 months. Honest post-mortem: **What we'd do the same:** - Running old and new suites in parallel for 2 months before cutting over - Treating the rewrite as a chance to delete tests (we cut 200 tests that were no longer valuable) - Documenting architectural decisions as we made them (finally have a test strategy doc) **What we'd do differently:** - Start with the test data layer, not the page objects. We rebuilt page objects twice because the data layer changed underneath them. - Migrate one service at a time, not all at once. Running two Playwright suites alongside each other was much cleaner than running Playwright + Selenium. - Set harder quality gates earlier. We allowed "good enough for now" test code early in the rewrite and spent the last 2 months cleaning it up. **The number that matters:** flake rate went from 8.3% to 0.9%. Worth the 8 months.