testWidgets with Store not working properly about mobx.dart HOT 3 CLOSED

// card_test.dart
import 'package:flutter/material.dart';
import 'package:flutter_mobx/flutter_mobx.dart';
import 'package:flutter_test/flutter_test.dart';

import 'counter_store.dart';

void main() {
  testWidgets('Card with incrementing count', (WidgetTester tester) async {
    final counterStore = CounterStore();

    await tester.pumpWidget(
      Directionality(
        textDirection: TextDirection.ltr,
        child: Observer(
          builder: (_) => Text(
            '${counterStore.count}',
          ),
        ),
      ),
    );

    counterStore.increment();
    await tester.pump();

    expect(find.text('1'), findsOneWidget);
  });
}