packages/flutter/test/widgets/grid_view_layout_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/widgets.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('Empty GridView', (WidgetTester tester) async {
    final List<Widget> children = <Widget>[
      const DecoratedBox(decoration: BoxDecoration()),
      const DecoratedBox(decoration: BoxDecoration()),
      const DecoratedBox(decoration: BoxDecoration()),
      const DecoratedBox(decoration: BoxDecoration()),
    ];

    await tester.pumpWidget(
      Directionality(
        textDirection: TextDirection.ltr,
        child: Center(
          child: SizedBox(
            width: 200.0,
            child: GridView.extent(
              maxCrossAxisExtent: 100.0,
              shrinkWrap: true,
              children: children,
            ),
          ),
        ),
      ),
    );

    expect(tester.renderObjectList<RenderBox>(find.byType(DecoratedBox)), hasLength(4));

    for (final RenderBox box in tester.renderObjectList<RenderBox>(find.byType(DecoratedBox))) {
      expect(box.size.width, equals(100.0), reason: 'child width');
      expect(box.size.height, equals(100.0), reason: 'child height');
    }

    final RenderBox grid = tester.renderObject(find.byType(GridView));
    expect(grid.size.width, equals(200.0), reason: 'grid width');
    expect(grid.size.height, equals(200.0), reason: 'grid height');

    expect(grid.debugNeedsLayout, false);

    await tester.pumpWidget(
      Directionality(
        textDirection: TextDirection.ltr,
        child: Center(
          child: SizedBox(
            width: 200.0,
            child: GridView.extent(
              maxCrossAxisExtent: 60.0,
              shrinkWrap: true,
              children: children,
            ),
          ),
        ),
      ),
    );

    for (final RenderBox box in tester.renderObjectList<RenderBox>(find.byType(DecoratedBox))) {
      expect(box.size.width, equals(50.0), reason: 'child width');
      expect(box.size.height, equals(50.0), reason: 'child height');
    }

    expect(grid.size.width, equals(200.0), reason: 'grid width');
    expect(grid.size.height, equals(50.0), reason: 'grid height');
  });
}