Golden Files testing in Flutter

golden_files_test.dart

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

void main() {
  setUp(() {
    // Limits viewport in tests to size of 100, 100 to decrease the size of
    // the pngs
    WidgetsBinding.instance.renderView.configuration =
        TestViewConfiguration(size: const Size(100, 100));
  });
  testWidgets('Golden file testing', (tester) async {
    // RepaintBoundary is needed to optimize the png
    await tester.pumpWidget(RepaintBoundary(child: MyWidget(0)));

    await tester.pumpAndSettle();

    await expectLater(
      find.byType(RepaintBoundary),
      matchesGoldenFile('golden-file.png'),
    );
  });
}

class MyWidget extends StatelessWidget {
  const MyWidget(this.radius, {Key key}) : super(key: key);

  final double radius;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(8),
      child: Container(
        decoration: BoxDecoration(
          border: Border.all(
            width: 12,
            color: Color(0xFF01579B),
          ),
          borderRadius: BorderRadius.all(Radius.circular(radius)),
        ),
        child: FlutterLogo(),
      ),
    );
  }
}