fix: apply code review

test/helpers/mock_flame_images.dart

@@ -8,17 +8,23 @@ import 'package:mocktail/mocktail.dart';
 
 class _MockImages extends Mock implements Images {}
 
-Future<void> mockFlameImages() async {
+/// {@template mock_flame_images}
+/// Mock for flame images instance.
+///
+/// Using real images blocks the tests, for this reason we need fake image
+/// everywhere we use [Images.fromCache] or [Images.load].
+/// {@endtemplate}
 // TODO(arturplaczek): need to find for a better solution for loading image
 // or use original images.
-  final image = await decodeImageFromList(Uint8List.fromList(fakeImage));
+Future<void> mockFlameImages() async {
+  final image = await decodeImageFromList(Uint8List.fromList(_fakeImage));
   final images = _MockImages();
   when(() => images.fromCache(any())).thenReturn(image);
   when(() => images.load(any())).thenAnswer((_) => Future.value(image));
   Flame.images = images;
 }
 
-const fakeImage = <int>[
+const _fakeImage = <int>[
   0x89,
   0x50,
   0x4E,