test/widget_test.dart

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

import 'package:chapter_04/main.dart';

// リスト 7.7
Widget _createCountPage() => MaterialApp(home: CountPage());

void main() {
  testWidgets('Count Page Widget Tests', (WidgetTester tester) async {
    await tester.pumpWidget(_createCountPage());
    expect(find.text('カウント'), findsOneWidget);
    await tester.tap(find.byIcon(Icons.add));
    await tester.pump();
    expect(find.text('1'), findsOneWidget);
    await tester.tap(find.byIcon(Icons.remove));
    await tester.pump();
    expect(find.text('0'), findsOneWidget);
  });
}