old_contents: import factory
  from django.contrib.auth.models import User
  from django.utils.timezone import now
  
  class UserFactory(factory.DjangoModelFactory):
      FACTORY_FOR = User
  
      first_name = 'DRF'
      last_name = 'Test'
      username = 'drftest'
      password = 'drftest'
      is_active = True
      is_superuser = False
      last_login = now()
      date_joined = now()
  
new_contents: import factory
  from django.contrib.auth.models import User
  from django.utils.timezone import now
  from shop.models import (Product, Stamp, Order, OrderDetails, Voucher)
  
  
  class UserFactory(factory.DjangoModelFactory):
      FACTORY_FOR = User
  
      first_name = 'DRF'
      last_name = 'Test'
      username = 'drftest'
      password = 'drftest'
      is_active = True
      is_superuser = False
      last_login = now()
      date_joined = now()
  
  
  class ProductFactory(factory.DjangoModelFactory):
      FACTORY_FOR = Product
  
      name = "Product 1"
      collect_stamp = True
  
  
  class StampFactory(factory.DjangoModelFactory):
      FACTORY_FOR = Stamp
  
      user = factory.SubFactory(UserFactory)
      redeemed = False
  
  
  class OrderFactory(factory.DjangoModelFactory):
      FACTORY_FOR = Order
  
      user = factory.SubFactory(UserFactory)
      date = now()
  
  
  class OrderDetailsFactory(factory.DjangoModelFactory):
      FACTORY_FOR = OrderDetails
  
      order = factory.SubFactory(OrderFactory)
      product = factory.SubFactory(ProductFactory)
      quantity = 4
  
  
  class VoucherFactory(factory.DjangoModelFactory):
      FACTORY_FOR = Voucher
  
      user = factory.SubFactory(UserFactory)
      redeemed = False
  
subject: Add factories for unit testing