packages/flutter/test/widgets/page_storage_test.dart

// Copyright 2014 The Flutter 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/material.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('PageStorage read and write', (WidgetTester tester) async {
    const Key builderKey = PageStorageKey<String>('builderKey');
    late StateSetter setState;
    int storedValue = 0;

    await tester.pumpWidget(
      MaterialApp(
        home: StatefulBuilder(
          key: builderKey,
          builder: (BuildContext context, StateSetter setter) {
            PageStorage.of(context)!.writeState(context, storedValue);
            setState = setter;
            return Center(
              child: Text('storedValue: $storedValue'),
            );
          },
        ),
      ),
    );

    final Element builderElement = tester.element(find.byKey(builderKey));
    expect(PageStorage.of(builderElement), isNotNull);
    expect(PageStorage.of(builderElement)!.readState(builderElement), equals(storedValue));

    setState(() {
      storedValue = 1;
    });
    await tester.pump();
    expect(PageStorage.of(builderElement)!.readState(builderElement), equals(storedValue));
  });

  testWidgets('PageStorage read and write by identifier', (WidgetTester tester) async {
    late StateSetter setState;
    int storedValue = 0;

    Widget buildWidthKey(Key key) {
      return MaterialApp(
        home: StatefulBuilder(
          key: key,
          builder: (BuildContext context, StateSetter setter) {
            PageStorage.of(context)!.writeState(context, storedValue, identifier: 123);
            setState = setter;
            return Center(
              child: Text('storedValue: $storedValue'),
            );
          },
        ),
      );
    }

    Key key = const Key('Key one');
    await tester.pumpWidget(buildWidthKey(key));
    Element builderElement = tester.element(find.byKey(key));
    expect(PageStorage.of(builderElement), isNotNull);
    expect(PageStorage.of(builderElement)!.readState(builderElement), isNull);
    expect(PageStorage.of(builderElement)!.readState(builderElement, identifier: 123), equals(storedValue));

    // New StatefulBuilder widget - different key - but the same PageStorage identifier.

    key = const Key('Key two');
    await tester.pumpWidget(buildWidthKey(key));
    builderElement = tester.element(find.byKey(key));
    expect(PageStorage.of(builderElement), isNotNull);
    expect(PageStorage.of(builderElement)!.readState(builderElement), isNull);
    expect(PageStorage.of(builderElement)!.readState(builderElement, identifier: 123), equals(storedValue));

    setState(() {
      storedValue = 1;
    });
    await tester.pump();
    expect(PageStorage.of(builderElement)!.readState(builderElement, identifier: 123), equals(storedValue));
  });

}