feat: add rows count (broken), fix: bug with low stock items

test/bar_screen_view_model_test.dart

@@ -0,0 +1,64 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:kooltab2/models/product.dart';
+import 'package:kooltab2/models/tab_item.dart';
+import 'package:kooltab2/services/bar_tab_service.dart';
+import 'package:kooltab2/services/product_service.dart';
+import 'package:kooltab2/viewmodels/bar_screen_view_model.dart';
+import 'package:kooltab2/viewmodels/inventory_view_model.dart';
+import 'package:mocktail/mocktail.dart';
+
+class MockBarTabService extends Mock implements BarTabService {}
+
+class MockProductService extends Mock implements ProductService {}
+
+void main() {
+  late MockBarTabService barTabService;
+  late MockProductService productService;
+  late InventoryViewModel inventory;
+  late BarScreenViewModel viewModel;
+
+  setUp(() {
+    barTabService = MockBarTabService();
+    productService = MockProductService();
+    inventory = InventoryViewModel(productService: productService);
+    viewModel = BarScreenViewModel(
+      barTabService: barTabService,
+      inventory: inventory,
+    );
+  });
+
+  test(
+    'does not increase a tab item when its product is out of stock',
+    () async {
+      const product = Product(
+        id: 'prod-1',
+        name: 'Chips',
+        category: 'Snacks',
+        stockQuantity: 0,
+        lowStockThreshold: 5,
+        priceInCents: 150,
+      );
+      const item = TabItem(
+        id: 'item-1',
+        tabId: 'tab-1',
+        productId: 'prod-1',
+        productName: 'Chips',
+        quantity: 20,
+        unitPriceInCents: 150,
+      );
+
+      when(
+        () => productService.getProducts(),
+      ).thenAnswer((_) async => [product]);
+      await inventory.load();
+
+      await expectLater(
+        viewModel.changeItemQuantity(item, 21),
+        throwsA(isA<InsufficientStockException>()),
+      );
+
+      expect(viewModel.errorMessage, isNull);
+      verifyNoMoreInteractions(barTabService);
+    },
+  );
+}

test/product_service_test.dart

@@ -218,7 +218,7 @@ void main() {
 
         expect(
           () => service.decreaseStock('low-stock', 5),
-          throwsA(isA<Exception>()),
+          throwsA(isA<InsufficientStockException>()),
         );
       });
     });