How do you properly test navigation logic, including verifying that a specific given route correctly and reliably navigates to its own expected screen and that a redirect properly and correctly occurs when genuinely expected?

Testing navigation logic typically involves writing widget tests that properly pump your app configured with a genuine test router instance, then simulating navigation by properly tapping a specific given link or button, and verifying that the genuinely correct expected destination screen actually properly appears, and separately testing your router's own specific redirect logic in isolation by directly calling it with several different genuinely simulated authentication states, confirming it returns the exact genuinely correct expected redirect path or properly returns null when no redirect should actually genuinely occur at all.

testWidgets('navigating to product detail shows correct screen', (tester) async {
  await tester.pumpWidget(MaterialApp.router(routerConfig: router));
  await tester.tap(find.text('View Product'));
  await tester.pumpAndSettle();
  expect(find.byType(ProductScreen), findsOneWidget);
});