Flutter Testing LateInitializationError in my class? - flutter

Question

I have a class that helps me handle the sharedpreferences:
class SharedPref {
static late final SharedPreferences prefs;
static initialize() async {
prefs = await SharedPreferences.getInstance();
}
SharedPref._();
static Future<void> save(String key, String value) async {
await prefs.setString(key, value);
}
// more methods that help me to save/load values...
}
Then I have a testing function:
class MockNavigatorObserver extends Mock implements NavigatorObserver {}
void main() {
testWidgets('Button is present and triggers navigation after tapped',
(WidgetTester tester) async {
final mockObserver = MockNavigatorObserver();
await tester.pumpWidget(
MaterialApp(
home: FirstPage(),
navigatorObservers: [mockObserver],
),
);
expect(find.byType(RaisedButton), findsOneWidget);
await tester.tap(find.byType(RaisedButton));
await tester.pumpAndSettle();
expect(find.byType(MyDetailedPage), findsOneWidget);
});
}
Whenever I run the test:
The following LateError was thrown running a test:
LateInitializationError: Field 'prefs' has not been initialized.
How am I supposed to initialize that? I called the SharedPref.initialize(); before the final mockObserver... but made no change.
Thanks in advance.

Answer 1

I called the SharedPref.initialize(); before
You need to await the call, otherwise you have race conditions when your save is called and initalize may or may not already be finished.

Answer 2

As you mentioned problem was in
final mockObserver = MockNavigatorObserver();
not inside main() function.
But it was another silly mistake with this kind error if wright initialisation like this:
late final MockNavigatorObserver mockObserver;
setUp(() {
mockObserver= MockNavigatorObserver();
})
Problem in this case is using final keyword. If use like that, only one test will pass. You need not using final keyword, instead:
late MockNavigatorObserver mockObserver;
setUp(() {
mockObserver= MockNavigatorObserver();
})