Flutter Unit Test With Localization

Question

I have a utility class that relies on the context in order to translate the output. Something along the lines of :

static String doSomeLogicAndTranslate(String firstArg, BuildContext context) {
    //...
    return AppLocalizations.of(context)!.someKey;
}

Now, I want to be able to write some unit tests for this class, but since the second argument is the context, I'm having a hard time doing so.

What I have tried so far:

• Mocking a BuildContext with Mockito (as described here) and passing that as the second argument --> Doesn't work as inside the localizations.dart file it returns null here

    static T? of<T>(BuildContext context, Type type) {
        final _LocalizationsScope? scope = context.dependOnInheritedWidgetOfExactType<_LocalizationsScope>();  /// Scope is null here
        return scope?.localizationsState.resourcesFor<T?>(type);
    }
  

I have tried looking around for any other solutions for this, but have not found anything substantial. This seems like it should be pretty straight forward, but it isn't.

Answer 1

My first suggestion would be to remove the dependency on BuildContext altogether by passing AppLocalizations directly to your function:

static String doSomeLogicAndTranslate(String firstArg, AppLocalizations loc) {
    //...
    return loc.someKey;
}

test('AppLocalizations test', () {
  final loc = lookupAppLocalizations(const Locale('en'));
  final output = doSomeLogicAndTranslate('some arg', loc);
  // Calls to expect or whatever here
});

If that's not possible for some reason, you can use testWidgets to set up a minimal widget tree and retrieve a valid build context for the rest of your test from there:

testWidgets('AppLocalizations test', (tester) async {
  await tester.pumpWidget(
    Localizations(
      locale: const Locale('en'), // Or whichever locale you prefer to test with
      delegates: AppLocalizations.localizationsDelegates,
      child: Container(),
    ),
  );
  final BuildContext context = tester.element(find.byType(Container));
  final output = doSomeLogicAndTranslate('some arg', context);
  // Calls to expect or whatever here
});