Why Playwright Tests Still Flake and How Systems Engineering Can Fix It

Automation engineers often dismiss unreliable tests as random flakiness, but the root cause is a measurable race condition called the 'Determinism Gap' — the window between when a test asserts application state and when that state finishes changing. Sources of this gap include network latency, rendering delays, shared database state, and CPU contention on CI runners. While Playwright's built-in actionability checks eliminate many interaction-side failures that plagued older tools like Selenium, they do not address assertion-side gaps where tests verify symptoms rather than actual outcomes. For example, asserting that a success toast appears does not confirm a server-side save completed, since optimistic UI can render before the network request resolves. Engineers are advised to intercept network responses directly and assert on server-confirmed state, making invisible transitions visible and closing the gap rather than masking it with retries.