fix: tests

Author: Alexays

test/layer/circle_layer_test.dart

@@ -23,7 +23,10 @@ void main() {
 
     await tester.pumpWidget(TestApp(circles: circles));
     expect(find.byType(FlutterMap), findsOneWidget);
-    expect(find.byType(CircleLayer), findsWidgets);
-    expect(find.byKey(key), findsOneWidget);
+    expect(find.byType(CircleLayer), findsOneWidget);
+
+    // Assert that batching works and all circles are drawn into the same
+    // CustomPaint/Canvas.
+    expect(find.descendant(of: find.byType(CircleLayer), matching: find.byType(CustomPaint)), findsOneWidget);
   });
 }