TestLocalizedWidget.dart

class TestLocalizationsDelegate
		extends LocalizationsDelegate<TestLocalizations> {
	const TestLocalizationsDelegate();
	
	@override
	bool isSupported(Locale locale) {
		return [DE, EN, PL].contains(locale.languageCode);
	}
	
	@override
	Future<TestLocalizations> load(Locale locale) {
		return TestLocalizations.load(locale);
	}
	
	@override
	bool shouldReload(LocalizationsDelegate<TestLocalizations> old) => false;
}

class TestLocalizations {
	static Future<TestLocalizations> load(Locale locale) async {
		final String localeName =
		locale.countryCode == null || locale.countryCode.isEmpty
				? locale.languageCode
				: locale.toString();
		
		final String canonicalLocaleName = Intl.canonicalizedLocale(localeName);
		print("localName: $localeName");
		print("canonicalLocaleName: $canonicalLocaleName");
		
		await initializeMessages(canonicalLocaleName);
		
		return TestLocalizations();
	}
	
	static TestLocalizations of(BuildContext context) {
		return Localizations.of<TestLocalizations>(
				context, TestLocalizations);
	}
	
	String get title => Intl.message('Test title', name: 'title');
	String get message => Intl.message('Test message', name: 'message');
}

class MyTestWidget extends StatelessWidget {
	final String title;
	final String message;
	
	const MyTestWidget({
		Key key,
		@required this.title,
		@required this.message,
	}) : super(key: key);
	
	@override
	Widget build(BuildContext context) {
		return MaterialApp(
			title: "My Test App",
			home: Scaffold(
				appBar: AppBar(
					title: Text(title),
				),
				body: Center(
					child: Text(message),
				),
			),
		);
	}
}

void main() {
	
	Widget withLocalizations({Widget child}) => Localizations(
		child: child,
		locale: Locale(EN),
		delegates: [
			const TestLocalizationsDelegate(),
			GlobalWidgetsLocalizations.delegate,
		],
	);
	
	testWidgets("Localizations", (WidgetTester tester) async {
		// runAsync is not necessary in this case
		await tester.runAsync(() async {
			String title = "T", message = "M";
			await tester.pumpWidget(withLocalizations(child: Builder(
				builder: (context) {
					final loc = TestLocalizations.of(context);
					title = loc.title;
					message = loc.message;
					return MyTestWidget(title: title, message: message);
				},
			))); // localizationsWrap(
			await tester.pumpAndSettle();
			final titleFinder = find.text(title);
			final messageFinder = find.text(message);
			expect(titleFinder, findsOneWidget);
			expect(messageFinder, findsOneWidget);
		});
	});
}