test(e2e): virtual scroll over 50 000 rows

test/e2e/03_data_grid_and_mutations/e2e_grid_virtual_scroll_test.dart

@@ -0,0 +1,91 @@
+import 'package:flutter/material.dart' as material;
+import 'package:flutter_test/flutter_test.dart';
+import 'package:querya_desktop/features/workspace/result_grid_view.dart';
+
+import '../../support/querya_theme_test_shell.dart';
+
+const _timeout = Timeout(Duration(seconds: 120));
+const _rowCount = 50000;
+
+int _builtRows() => find
+    .byWidgetPredicate((w) =>
+        w.key is material.ValueKey &&
+        '${(w.key as material.ValueKey).value}'.startsWith('result-row-'))
+    .evaluate()
+    .length;
+
+material.ScrollController _verticalController(WidgetTester tester) {
+  final scrollable = tester.widget<material.Scrollable>(
+    find
+        .byWidgetPredicate((w) =>
+            w is material.Scrollable && w.axis == material.Axis.vertical)
+        .first,
+  );
+  return scrollable.controller!;
+}
+
+void main() {
+  Future<dynamic> open(WidgetTester tester) async {
+    await tester.binding.setSurfaceSize(const material.Size(1000, 700));
+    addTearDown(() => tester.binding.setSurfaceSize(null));
+    final rows = List.generate(_rowCount, (i) => ['$i', 'Value $i']);
+    await tester.pumpWidget(
+      queryaThemeTestShell(
+        child: material.Scaffold(
+          body: material.SizedBox(
+            width: 1000,
+            height: 600,
+            child: VirtualResultGrid(columns: const ['id', 'value'], rows: rows),
+          ),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+    return tester.state(find.byType(VirtualResultGrid));
+  }
+
+  testWidgets('50 000 rows build only what the viewport shows',
+      timeout: _timeout, (tester) async {
+    await open(tester);
+
+    expect(find.text('Value 0'), findsOneWidget);
+    expect(find.text('Value 49999'), findsNothing);
+    expect(_builtRows(), lessThan(100));
+  });
+
+  testWidgets('fast scrolling keeps the widget count and cache bounded',
+      timeout: _timeout, (tester) async {
+    final dynamic state = await open(tester);
+
+    for (var i = 0; i < 30; i++) {
+      await tester.fling(
+        find.byType(VirtualResultGrid),
+        const material.Offset(0, -800),
+        6000,
+      );
+      await tester.pump(const Duration(milliseconds: 100));
+      expect(_builtRows(), lessThan(100), reason: 'after fling $i');
+    }
+    await tester.pumpAndSettle();
+
+    expect(find.text('Value 0'), findsNothing);
+    expect(state.rowWidgetsCacheCount, lessThanOrEqualTo(200));
+  });
+
+  testWidgets('the last row is reachable and scrolling back restores the first',
+      timeout: _timeout, (tester) async {
+    await open(tester);
+    final controller = _verticalController(tester);
+
+    controller.jumpTo(controller.position.maxScrollExtent);
+    await tester.pumpAndSettle();
+    expect(find.text('Value 49999'), findsOneWidget);
+    expect(find.text('Value 0'), findsNothing);
+    expect(_builtRows(), lessThan(100));
+
+    controller.jumpTo(0);
+    await tester.pumpAndSettle();
+    expect(find.text('Value 0'), findsOneWidget);
+    expect(find.text('Value 49999'), findsNothing);
+  });
+}