def test_to_sorted_doubly_linked_list(self): self.class_under_test.insert(1) self.class_under_test.insert(3) self.class_under_test.insert(4) self.class_under_test.insert(2) result = b.to_sorted_doubly_linked_list(self.class_under_test) self.assertTrue(result.head.data == 1) self.assertTrue(result.head.prev.data == 4)