def test_equal_1(self):
     self.assertEqual(maps([1, 2, 3]), [2, 4, 6])
 def test_equal_2(self):
     self.assertEqual(maps([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]),
                      [0, 2, 4, 6, 8, 10, 12, 14, 16, 18])
 def test_equal_3(self):
     self.assertEqual(maps([]), [])