old_contents: from django.test import UnitTest
  from django.test import Client
  
  
  class TestAPI(UnitTest):
      def setUp(self):
          self.client = Client()
  
      def test_api(self):
          pass
  
new_contents: from django.test import TestCase
  from django.test import Client
  
  
  class TestAPI(TestCase):
      def setUp(self):
          self.client = Client()
  
      def test_api(self):
          pass
  
subject: Fix import.