test: wrote tests for platform detection on how to play dialog

test/start_game/widgets/how_to_play_dialog_test.dart

@@ -1,39 +1,59 @@
 // ignore_for_file: prefer_const_constructors
 
-import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:mocktail/mocktail.dart';
 import 'package:pinball/l10n/l10n.dart';
 import 'package:pinball/start_game/start_game.dart';
+import 'package:platform_helper/platform_helper.dart';
 
 import '../../helpers/helpers.dart';
 
+class MockPlatformHelper extends Mock implements PlatformHelper {}
+
 void main() {
   group('HowToPlayDialog', () {
     late AppLocalizations l10n;
+    late PlatformHelper platformHelper;
 
     setUp(() async {
       l10n = await AppLocalizations.delegate.load(Locale('en'));
+      platformHelper = MockPlatformHelper();
     });
 
-    testWidgets('displays content for desktop', (tester) async {
-      debugDefaultTargetPlatformOverride = TargetPlatform.macOS;
+    testWidgets(
+      'can be instantiated without passing in a platform helper',
+      (tester) async {
         await tester.pumpApp(HowToPlayDialog());
+        expect(find.byType(HowToPlayDialog), findsOneWidget);
+      },
+    );
+
+    testWidgets('displays content for desktop', (tester) async {
+      when(() => platformHelper.isMobile).thenAnswer((_) => false);
+      await tester.pumpApp(
+        HowToPlayDialog(
+          platformHelper: platformHelper,
+        ),
+      );
       expect(find.text(l10n.howToPlay), findsOneWidget);
       expect(find.text(l10n.tipsForFlips), findsOneWidget);
       expect(find.text(l10n.launchControls), findsOneWidget);
       expect(find.text(l10n.flipperControls), findsOneWidget);
-      debugDefaultTargetPlatformOverride = null;
+      expect(find.byType(KeyButton), findsNWidgets(7));
     });
 
     testWidgets('displays content for mobile', (tester) async {
-      debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
-      await tester.pumpApp(HowToPlayDialog());
+      when(() => platformHelper.isMobile).thenAnswer((_) => true);
+      await tester.pumpApp(
+        HowToPlayDialog(
+          platformHelper: platformHelper,
+        ),
+      );
       expect(find.text(l10n.howToPlay), findsOneWidget);
       expect(find.text(l10n.tipsForFlips), findsOneWidget);
       expect(find.text(l10n.tapAndHoldRocket), findsOneWidget);
       expect(find.text(l10n.tapLeftRightScreen), findsOneWidget);
-      debugDefaultTargetPlatformOverride = null;
     });
   });