code: def test_handle_unknown_have_new_value_expect_negative_1(self):
      # See #238
      train = pd.DataFrame({"city": ["chicago", "st louis"]})
      test = pd.DataFrame({"city": ["chicago", "los angeles"]})
      expected = [1.0, -1.0]
  
      enc = encoders.OrdinalEncoder(handle_missing="return_nan")
      enc.fit(train)
      result = enc.transform(test)["city"].tolist()
  
      self.assertEqual(expected, result)
  
imports: import pandas
  from unittest import TestCase
  import tests.helpers
  import numpy
  import category_encoders
label_desc: Use image node_id 6 for calling the TestOrdinalEncoder obj's underlying member method code with example usage: obj.test_handle_unknown_have_new_value_expect_negative_1() without return types