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7.6When to Test on Real Browsers vs Engine Equivalents
| Scenario | Real Browser Needed? | Why |
|---|---|---|
| CSS rendering differences | No -- engine test sufficient | Same engine = same rendering |
| Form auto-fill behavior | Yes | Browser-specific UI overlays |
| Extension conflicts | Yes | Extensions are browser-specific |
| Download/print behavior | Yes | Browser-specific dialogs |
| PWA install prompts | Yes | Different in Chrome, Edge, Safari |
| WebRTC video calling | Yes | Implementation differences per browser |
| Payment request API | Yes | Different UI per browser |
Playwright's WebKit engine is a close but not identical approximation of Safari. For most web testing, it is sufficient. For Safari-specific features (media playback, WebKit-only CSS, Share Sheet), test on real Safari via BrowserStack.
The three-tier strategy balances thoroughness with practicality. Tier 1 catches 95% of cross-browser bugs. Tier 2 catches the mobile-specific issues. Tier 3 is insurance against long-tail edge cases.