Simplify Golden Testing with Alchemist - A Flutter Package

Introduction:

Golden testing is an essential part of ensuring the visual correctness of Flutter applications. However, writing and running golden tests can be challenging and time-consuming. Fortunately, there's a Flutter package called Alchemist that aims to simplify golden testing and make it easier for developers. In this article, we will explore the features and usage of the Alchemist package, along with some advanced techniques for effective golden testing.

Golden Testing Made Easy with Alchemist:

Alchemist is a Flutter package specifically designed to support golden testing. It provides functions, extensions, and documentation that streamline the golden testing process. Inspired by the golden_toolkit package from eBay Motors, Alchemist aims to make writing and running golden tests in Flutter a breeze.

Platform Tests vs. CI Tests:

Alchemist offers two types of golden tests: platform tests and CI tests. Platform tests generate golden files with human-readable text, making them suitable for local testing. On the other hand, CI tests replace text blocks with colored squares to ensure consistent output across different platforms. This distinction is crucial because text rendering can vary across platforms, potentially causing CI systems to fail the test. By using CI tests with colored squares, Alchemist eliminates this platform dependency and ensures consistent test results.

Basic Usage of Alchemist:

To get started with Alchemist, you need to add the package to your Flutter project. Once added, you can write golden tests using the goldenTest function. It's recommended to group related golden tests into a test group to keep them organized.

import 'package:flutter_test/flutter_test.dart';
import 'package:alchemist/alchemist.dart';

void main() {
  group('ListTile golden tests', () {
    testGoldens('default ListTile', (tester) async {
      await tester.pumpWidget(const ListTile(
        leading: Icon(Icons.ac_unit),
        title: Text('Default ListTile'),
        subtitle: Text('This is a default ListTile'),
      ));

      await screenMatchesGolden(tester, 'default_list_tile');
    });

    testGoldens('ListTile with custom colors', (tester) async {
      await tester.pumpWidget(
        const ListTile(
          leading: Icon(Icons.ac_unit),
          title: Text('Custom ListTile'),
          subtitle: Text('This is a custom ListTile'),
        ).withCustomColors(
          backgroundColor: Colors.blue,
          titleColor: Colors.white,
          subtitleColor: Colors.white70,
        ),
      );

      await screenMatchesGolden(tester, 'custom_list_tile');
    });
  });
}
    

Advanced Techniques:

Alchemist provides several advanced techniques to enhance golden testing in Flutter applications. Let's explore some of these techniques:

Parameterized Tests:

You can use parameterized tests with Alchemist to run the same golden test with different input parameters. This allows you to test various scenarios and configurations efficiently. By leveraging the power of parameterized tests, you can increase the coverage of your golden tests without duplicating code.

testGoldens('ListTile with different colors', (tester) async {
  for (var i = 0; i < colors.length; i++) {
    final color = colors[i];
    await tester.pumpWidget(
      const ListTile(
        leading: Icon(Icons.ac_unit),
        title: Text('Custom ListTile'),
        subtitle: Text('This is a custom ListTile'),
      ).withCustomColors(
        backgroundColor: color,
        titleColor: color == Colors.black ? Colors.white : Colors.black,
        subtitleColor: color == Colors.black ? Colors.white70 : Colors.black54,
      ),
    );

    await screenMatchesGolden(tester, 'custom_list_tile_$i');
  }
});
    

Widget Testing:

Alchemist integrates seamlessly with Flutter's widget testing framework, allowing you to combine widget testing and golden testing. You can write widget tests that exercise your widgets and then validate their visual appearance using golden tests. This combination ensures both functional correctness and visual consistency.

testWidgets('CounterButton increments counter', (tester) async {
  await tester.pumpWidget(CounterButton());

  await tester.tap(find.byType(ElevatedButton));
  await tester.pump();

  expect(find.text('1'), findsOneWidget);
  await screenMatchesGolden(tester, 'counter_button');
});
    

Custom Matchers:

Alchemist allows you to define custom matchers to check specific aspects of the rendered UI. You can create matchers that validate the presence or absence of certain widgets, specific layout configurations, or any other criteria relevant to your golden tests. Custom matchers enable you to write more expressive and focused golden tests.

Matcher isWidgetOfType(Type type) {
  return find.byWidgetPredicate((widget) => widget.runtimeType == type);
}

testGoldens('MyCustomWidget golden test', (tester) async {
  await tester.pumpWidget(MyCustomWidget());

  expect(find.text('Hello, World!'), findsOneWidget);
  expect(find.byType(MyCustomWidget), isWidgetOfType(MyCustomWidget));
  expect(find.byType(Text), findsOneWidget);

  await screenMatchesGolden(tester, 'my_custom_widget');
});
    

Conclusion:

Golden testing is crucial for ensuring visual correctness and consistency in Flutter applications. Alchemist simplifies the golden testing process by providing a comprehensive set of tools and features specifically designed for Flutter developers. By leveraging Alchemist, you can streamline your golden testing workflow, save time, and improve the overall quality of your Flutter applications.