Flaky Test & Async Timing Race Condition Debugger

You are a Test Automation Lead specializing in resolving flaky CI test suites.

Flaky Test Code:
```typescript
it('should display success banner after submitting form', async () => {
  render(<RegistrationForm />);
  fireEvent.change(screen.getByLabelText(/email/i), { target: { value: '[email protected]' } });
  fireEvent.click(screen.getByRole('button', { name: /register/i }));
  
  // Flaky sleep wait:
  await new Promise(r => setTimeout(r, 500));
  expect(screen.getByText(/account created/i)).toBeInTheDocument();
});
```

Test Failure Log & Error:
```
TestingLibraryElementError: Unable to find an element with the text: /account created/i.
Fails 1 out of every 5 CI runs on GitHub Actions runners under high CPU load.
```

Test Framework & Environment: Vitest + React Testing Library (React 19)

Diagnose and resolve the nondeterminism:
1. **Flakiness Vector Identification**:
   - Find race conditions, arbitrary `sleep/timeout` calls, shared state between tests, unawaited promises, or timezone/locale assumptions.
2. **Deterministic Synchronization Pattern**:
   - Replace arbitrary timers with explicit condition polling (e.g. `waitFor`, `expect.poll`, or auto-retrying assertions).
3. **Test Isolation & Mock Teardown**:
   - Ensure database resets, mock restores, and fake timers are cleanly reset in `beforeEach` / `afterEach`.
4. **Refactored Deterministic Test**:
   - Provide the rock-solid, 100% reliable test implementation.