new_contents: import unittest
  
  from sum_sector_ids import (extract_checksum,
                              create_checksum,
                              is_valid_checksum,
                              extract_sector_id,
                              sum_sector_ids)
  
  class TestSumSectorIds(unittest.TestCase):
      def setUp(self):
          self.valid_room_a = 'aaaaa-bbb-z-y-x-123[abxyz]'
          self.valid_room_b = 'a-b-c-d-e-f-g-h-987[abcde]'
          self.invalid_room = 'not-a-real-room-404[oarel]'
  
      def test_extract_checksum(self):
          assert extract_checksum(self.valid_room_a) == 'abxyz'
          assert extract_checksum(self.valid_room_b) == 'abcde'
          assert extract_checksum(self.invalid_room) == 'oarel'
  
      def test_create_checksum(self):
          assert create_checksum(self.valid_room_a) == 'abxyz'
          assert create_checksum(self.valid_room_b) == 'abcde'
          assert create_checksum(self.invalid_room) == 'aelor'
  
      def test_is_valid_checksum(self):
          assert is_valid_checksum(self.valid_room_a) == True
          assert is_valid_checksum(self.valid_room_b) == True
          assert is_valid_checksum(self.invalid_room) == False
  
      def test_extract_sector_id(self):
          assert extract_sector_id(self.valid_room_a) == '123'
          assert extract_sector_id(self.valid_room_b) == '987'
  
      def test_sum_sector_ids(self):
          assert sum_sector_ids([self.valid_room_a, self.valid_room_b,
                                 self.invalid_room]) == 1110
  
subject: Add tests for summing sector ids.