WidgetTester.ensureVisible cannot find widgets in a long list #61458
Description
The 'ensureVisible' unit test in packages/flutter_test/test/widget_tester_test.dart only deal with a very short list, where all elements are already in cache. If I change the unit test to below (either as a ListView or as in the commented part ListView.builder),
group('ensureVisible', () {
testWidgets('scrolls to make widget visible', (WidgetTester tester) async {
await tester.pumpWidget(
MaterialApp(
home: Scaffold(
body: ListView(
shrinkWrap: true,
children: <Widget>[
for (int i = 0; i < 50; i ++)
ListTile(title: Text('Item $i')),
],
),
// body: ListView.builder(,
// itemCount: 50,
// shrinkWrap: true,
// itemBuilder: (BuildContext context, int i) => ListTile(title: Text('Item $i')),
// ),
),
),
);
// Make sure widget isn't on screen
expect(find.text('Item 45', skipOffstage: true), findsNothing);
await tester.ensureVisible(find.text('Item 45', skipOffstage: false));
await tester.pumpAndSettle();
expect(find.text('Item 45', skipOffstage: true), findsOneWidget);
});
});It will fail with:
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following StateError was thrown running a test:
Bad state: No element
Compare to its equivalence in flutter_driver FlutterDriver.scrollUntilVisible, the alternative implementation scroll until it finds such a widget.
It might be useful to provide a similar API in WidgetTester.