flutter_flutter/packages/flutter/test/widget/duplicate_key_test.dart

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter_test/flutter_test.dart';
import 'package:flutter/widgets.dart';

class Item {
  GlobalKey key1 = new GlobalKey();
  GlobalKey key2 = new GlobalKey();

  @override
  String toString() => "Item($key1, $key2)";
}
List<Item> items = <Item>[new Item(), new Item()];

class StatefulLeaf extends StatefulWidget {
  StatefulLeaf({ GlobalKey key }) : super(key: key);

  @override
  StatefulLeafState createState() => new StatefulLeafState();
}

class StatefulLeafState extends State<StatefulLeaf> {
  void test() { setState(() { }); }

  @override
  Widget build(BuildContext context) => new Text('leaf');
}

class KeyedWrapper extends StatelessWidget {
  KeyedWrapper(this.key1, this.key2);

  Key key1, key2;

  @override
  Widget build(BuildContext context) {
    return new Container(
      key: key1,
      child: new StatefulLeaf(
        key: key2
      )
    );
  }
}

Widget builder() {
  return new Column(
    children: <Widget>[
      new KeyedWrapper(items[1].key1, items[1].key2),
      new KeyedWrapper(items[0].key1, items[0].key2)
    ]
  );
}

void main() {
  testWidgets('duplicate key smoke test', (WidgetTester tester) async {
    await tester.pumpWidget(builder());
    StatefulLeafState leaf = tester.firstState(find.byType(StatefulLeaf));
    leaf.test();
    await tester.pump();
    Item lastItem = items[1];
    items.remove(lastItem);
    items.insert(0, lastItem);
    await tester.pumpWidget(builder()); // this marks the app dirty and rebuilds it
  });
}