old_contents: from unittest.mock import Mock
  
  from tornado_sqlalchemy import MissingDatabaseSettingError, SessionMixin
  
  from ._common import BaseTestCase, User, db
  
  
  class SessionMixinTestCase(BaseTestCase):
      def test_mixin_ok(self):
          class GoodHandler(SessionMixin):
              def __init__(h_self):
                  h_self.application = Mock()
                  h_self.application.settings = {'db': db}
  
              def run(h_self):
                  with h_self.make_session() as session:
                      return session.query(User).count()
  
          self.assertEqual(GoodHandler().run(), 0)
  
      def test_mixin_no_session_factory(self):
          class BadHandler(SessionMixin):
              def __init__(h_self):
                  h_self.application = Mock()
                  h_self.application.settings = {}
  
              def run(h_self):
                  with h_self.make_session() as session:
                      return session.query(User).count()
  
          self.assertRaises(MissingDatabaseSettingError, BadHandler().run)
  
      def test_distinct_sessions(self):
          sessions = set()
  
          class Handler(SessionMixin):
              def __init__(h_self):
                  db.configure(url=self.db_url)
  
                  h_self.application = Mock()
                  h_self.application.settings = {'db': db}
  
              def run(h_self):
                  session = h_self.session
  
                  sessions.add(id(session))
                  value = session.query(User).count()
  
                  session.commit()
                  session.close()
  
                  return value
  
          Handler().run()
          Handler().run()
  
          self.assertEqual(len(sessions), 2)
  
new_contents: from unittest.mock import Mock
  
  from tornado_sqlalchemy import MissingDatabaseSettingError, SessionMixin
  
  from ._common import BaseTestCase, User, db
  
  
  class SessionMixinTestCase(BaseTestCase):
      def test_mixin_ok(self):
          class GoodHandler(SessionMixin):
              def __init__(h_self):
                  h_self.application = Mock()
                  h_self.application.settings = {'db': db}
  
              def run(h_self):
                  with h_self.make_session() as session:
                      return session.query(User).count()
  
          self.assertEqual(GoodHandler().run(), 0)
  
      def test_mixin_no_db(self):
          class BadHandler(SessionMixin):
              def __init__(h_self):
                  h_self.application = Mock()
                  h_self.application.settings = {}
  
              def run(h_self):
                  with h_self.make_session() as session:
                      return session.query(User).count()
  
          self.assertRaises(MissingDatabaseSettingError, BadHandler().run)
  
      def test_distinct_sessions(self):
          sessions = set()
  
          class Handler(SessionMixin):
              def __init__(h_self):
                  db.configure(url=self.db_url)
  
                  h_self.application = Mock()
                  h_self.application.settings = {'db': db}
  
              def run(h_self):
                  session = h_self.session
  
                  sessions.add(id(session))
                  value = session.query(User).count()
  
                  session.commit()
                  session.close()
  
                  return value
  
          Handler().run()
          Handler().run()
  
          self.assertEqual(len(sessions), 2)
  
subject: fix test name