[FLASK] disable "Mark all as read button" when there are no notifications (#15333)

* [Flask] disable "Mark all as read button" when there are no notifications

* Adding test case

* Addressing feedback

ui/pages/notifications/notification.test.js

@@ -64,9 +64,10 @@ describe('Notifications', () => {
       },
     };
 
-    const { getByText } = render(mockStore);
+    const { getByText, getByRole } = render(mockStore);
 
     expect(getByText('Nothing to see here.')).toBeDefined();
+    expect(getByRole('button', { name: 'Mark all as read' })).toBeDisabled();
   });
 });
 

ui/pages/notifications/notifications.js

@@ -99,6 +99,7 @@ export default function Notifications() {
           type="secondary"
           className="notifications__header_button"
           onClick={markAllAsRead}
+          disabled={unreadNotifications.length === 0}
         >
           {t('notificationsMarkAllAsRead')}
         </Button>