code: def test_HandleUnknown_HaveOnlyKnown_ExpectExtraColumn(self):
      train = ["A", "B"]
  
      encoder = encoders.HelmertEncoder(
          handle_unknown="indicator", handle_missing="value"
      )
      result = encoder.fit_transform(train)
  
      expected = [[1, -1, -1], [1, 1, -1]]
      self.assertEqual(result.to_numpy().tolist(), expected)
  
file_path: category_encoders/tests/test_helmert.py
imports: import pandas
  from unittest import TestCase
  import numpy
  import category_encoders
label_desc: Use image node_id 11 for calling the TestHelmertEncoder obj's underlying member method code with example usage: obj.test_HandleUnknown_HaveOnlyKnown_ExpectExtraColumn() without return types