lottie-flutter/test/screenshot_test.dart

import 'dart:io';
import 'package:flutter_test/flutter_test.dart';
import 'package:lottie/lottie.dart';
import 'package:path/path.dart' as p;

void main() {
  //TODO(xha): download all screenshots from lottie-android as golden screenshots
  // https://happo.io/api/a/27/p/27/reports/abe43ed3d2f25a3ea3c38b1740011cf84fea5e93-android28

  final animationPath = 'example/assets';

  var animations = <_Screenshot>[
    _Screenshot('AndroidWave.json'),
    _Screenshot('HamburgerArrow.json'),
    _Screenshot('HamburgerArrow.json', progress: 0.5),
    _Screenshot('HamburgerArrow.json', progress: 1.0),
    _Screenshot('Mobilo/A.json', progress: 0.5),
    _Screenshot('Mobilo/B.json', progress: 0.5),
    _Screenshot('Logo/LogoSmall.json', progress: 0.5),
    _Screenshot('lottiefiles/atm_link.json', progress: 1.0),
  ];
  for (var animation in animations) {
    testWidgets('Screenshot ${animation.name} at ${animation.progress}',
        (WidgetTester tester) async {
      var composition = await LottieComposition.fromBytes(
          File(p.join(animationPath, animation.name)).readAsBytesSync());

      var goldenName = animation.goldenName;

      await tester.pumpWidget(RawLottie(
        composition: composition,
        progress: animation.progress,
      ));
      await expectLater(
          find.byType(RawLottie),
          matchesGoldenFile(
              p.join('golden', p.dirname(animation.name), '$goldenName.png')));
    });
  }
}

class _Screenshot {
  final String name;
  final double progress;

  _Screenshot(this.name, {this.progress = 0.0});

  String get goldenName =>
      '${p.basenameWithoutExtension(name)}_${progress.toStringAsFixed(1).replaceAll('.', '_')}';
}