new_contents: from django.test import TestCase
  
  from maker.migrations.default_categories import DEFAULT_CATEGORIES
  from maker.models import Category
  
  
  class CategoryTestCase(TestCase):
  
      def test_pre_install(self):
          categories = Category.objects.all()
          self.assertEqual(len(DEFAULT_CATEGORIES), len(categories))
          for c in categories:
              self.assertTrue(c.name in DEFAULT_CATEGORIES)
  
      def test_str(self):
          category = Category.objects.get(name=DEFAULT_CATEGORIES[0])
          self.assertEqual(category.name, str(category))
  
subject: Add tests for Category model