old_contents: # -*- coding: utf-8 -*-
  import pytest
  
  from components.history.factories import HistoryFactory
  from components.history.models import History
  
  pytestmark = pytest.mark.django_db
  
  
  class TestHistories:
      def test_factory(self):
          factory = HistoryFactory()
          assert isinstance(factory, History)
  
      def test_deltas(self):
          history1 = HistoryFactory(sum=10)
          history2 = HistoryFactory(sum=20)
          history3 = HistoryFactory(sum=80)
          assert history1.delta == 0
          assert history2.delta == 10
          assert history3.delta == 60
  
new_contents: # -*- coding: utf-8 -*-
  import pytest
  
  from components.history.factories import HistoryFactory
  from components.history.models import History
  
  pytestmark = pytest.mark.django_db
  
  
  class TestHistories:
      def test_factory(self):
          factory = HistoryFactory()
          assert isinstance(factory, History)
  
      def test_deltas(self):
          history1 = HistoryFactory(sum=10)
          history2 = HistoryFactory(sum=20)
          history3 = HistoryFactory(sum=10)
          assert history1.delta == 0
          assert history2.delta == 10
          assert history3.delta == -10
  
subject: Strengthen the test... more?