test: aggiungi suite di test Flutter

Struttura specchia lib/features/:
- test/features/meal_planner/ — unit (DayPlan, MealPlan, provider) + widget (MealCard)
- test/features/converter/ — unit (ConversionEntry, formule rawToCooked/cookedToRaw)
- test/features/shopping_list/ — unit (ShoppingItem, provider) + widget (ShoppingItemTile)
- test/helpers/pump_app.dart — estensione PumpApp condivisa tra widget test
- integration_test/app_test.dart — e2e navigazione, shopping list, convertitore, meal planner

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/features/shopping_list/models/shopping_item_test.dart

@@ -0,0 +1,46 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:biteplan/features/shopping_list/models/shopping_item.dart';
+
+void main() {
+  group('ShoppingItem', () {
+    test('checked è false di default', () {
+      final item = ShoppingItem(id: '1', name: 'Pollo');
+      expect(item.checked, false);
+    });
+
+    test('copyWith() aggiorna solo il campo specificato', () {
+      final item = ShoppingItem(id: '1', name: 'Pollo');
+      final checked = item.copyWith(checked: true);
+      expect(checked.checked, true);
+      expect(checked.name, 'Pollo');
+      expect(checked.id, '1');
+    });
+
+    test('copyWith() non modifica lorigine', () {
+      final item = ShoppingItem(id: '1', name: 'Pollo');
+      item.copyWith(checked: true);
+      expect(item.checked, false);
+    });
+
+    test('JSON round-trip preserva tutti i campi', () {
+      const item = ShoppingItem(id: '42', name: 'Riso', checked: true);
+      final restored = ShoppingItem.fromJson(item.toJson());
+      expect(restored.id, '42');
+      expect(restored.name, 'Riso');
+      expect(restored.checked, true);
+    });
+
+    test('fromJson gestisce campo checked assente (default false)', () {
+      final item = ShoppingItem.fromJson({'id': '1', 'name': 'Pasta'});
+      expect(item.checked, false);
+    });
+
+    test('toJson produce la mappa corretta', () {
+      const item = ShoppingItem(id: '5', name: 'Zucchine', checked: false);
+      final json = item.toJson();
+      expect(json['id'], '5');
+      expect(json['name'], 'Zucchine');
+      expect(json['checked'], false);
+    });
+  });
+}