old_contents: import unittest
  
  from tools.utils import flatten
  
  
  class UtilsTests(unittest.TestCase):
      def test_flatten(self):
          data = [[1, 2], [3], [4, 5]]
          flattened = flatten(*data)
          self.assertEqual(flattened, [1, 2, 3, 4, 5])
  
new_contents: import unittest
  
  from tools.utils import flatten, intersection, is_unique
  
  
  class UtilsTests(unittest.TestCase):
      def test_flatten(self):
          self.assertEqual(
              flatten([1, 2], [3], [4, 5]),
              [1, 2, 3, 4, 5])
  
      def test_intersection_empty(self):
          self.assertEqual(
              intersection([1, 2], [3, 4]),
              set([]))
  
      def test_intersection_non_empty(self):
          self.assertEqual(
              intersection([1, 2, 3, 4], [2, 4]),
              set([2, 4]))
  
      def test_is_unique_true(self):
          self.assertEqual(
              is_unique((1, 2), [3], [4, 5]),
              True)
  
      def test_is_unique_false(self):
          self.assertEqual(
              is_unique([1, 2], [3], [3, 4, 5]),
              False)
  
subject: Add more utils tests