perf: optimize NotificationBell store subscription and add unit tests

src/app/components/notifications/NotificationBell.tsx

@@ -6,8 +6,7 @@ import { useNotificationStore } from '@/app/store/notificationStore';
 import NotificationCenter from '@/app/components/notifications/NotificationCenter';
 
 export default function NotificationBell() {
-  const { notifications } = useNotificationStore();
-  const unread = notifications.filter((n) => !n.read).length;
+  const unreadCount = useNotificationStore((s) => s.notifications.filter((n) => !n.read).length);
   const [open, setOpen] = useState(false);
   const rootRef = useRef<HTMLDivElement>(null);
 
@@ -38,9 +37,9 @@ export default function NotificationBell() {
         className="relative inline-flex items-center justify-center w-9 h-9 rounded-full border bg-white hover:bg-gray-50"
       >
         <Bell size={18} className="text-gray-700" />
-        {unread > 0 && (
+        {unreadCount > 0 && (
           <span className="absolute -top-1 -right-1 inline-flex items-center justify-center px-1.5 py-0.5 text-[10px] leading-none rounded-full bg-red-600 text-white">
-            {unread}
+            {unreadCount}
           </span>
         )}
       </button>

src/app/components/notifications/__tests__/NotificationBell.test.tsx

@@ -0,0 +1,74 @@
+import React from 'react';
+import { render, act } from '@testing-library/react';
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import NotificationBell from '../NotificationBell';
+import { useNotificationStore } from '@/app/store/notificationStore';
+import { Bell } from 'lucide-react';
+
+// Mock lucide-react to spy on Bell rendering
+vi.mock('lucide-react', async (importOriginal) => {
+  const original = await importOriginal<typeof import('lucide-react')>();
+  return {
+    ...original,
+    Bell: vi.fn((props) => <original.Bell {...props} />),
+  };
+});
+
+describe('NotificationBell', () => {
+  beforeEach(() => {
+    useNotificationStore.setState({ notifications: [] });
+    vi.clearAllMocks();
+  });
+
+  it('renders correctly and has 0 unread initially', () => {
+    const { queryByText } = render(<NotificationBell />);
+    expect(queryByText('1')).toBeNull();
+  });
+
+  it('renders only once (no extra re-render) when a read notification is added', () => {
+    const { queryByText } = render(<NotificationBell />);
+
+    // Check initial render count of Bell
+    expect(Bell).toHaveBeenCalledTimes(1);
+
+    // Add a read notification to the store
+    act(() => {
+      useNotificationStore.getState().addNotification({
+        id: '1',
+        message: 'Read notification',
+        type: 'info',
+        read: true,
+        title: 'Info',
+      });
+    });
+
+    // The unread count badge should not be present
+    expect(queryByText('1')).toBeNull();
+
+    // Since the notification was already read, the unread count did not change
+    // Therefore, the NotificationBell should NOT have re-rendered
+    expect(Bell).toHaveBeenCalledTimes(1);
+  });
+
+  it('re-renders when an unread notification is added (unread count changes)', () => {
+    const { getByText } = render(<NotificationBell />);
+    expect(Bell).toHaveBeenCalledTimes(1);
+
+    // Add an unread notification to the store
+    act(() => {
+      useNotificationStore.getState().addNotification({
+        id: '2',
+        message: 'Unread notification',
+        type: 'info',
+        read: false,
+        title: 'Info',
+      });
+    });
+
+    // The unread count badge should display '1'
+    expect(getByText('1')).toBeInTheDocument();
+
+    // Since the unread count changed, the component should re-render
+    expect(Bell).toHaveBeenCalledTimes(2);
+  });
+});