code: def test_helmert_2StringCols_ExpectCorrectOrder(self):
      train = pd.DataFrame(
          {
              "col1": [1, 2, 3, 4],
              "col2": ["A", "B", "C", "D"],
              "col3": [1, 2, 3, 4],
              "col4": ["A", "B", "C", "A"],
          },
          columns=["col1", "col2", "col3", "col4"],
      )
      expected_columns = [
          "intercept",
          "col1",
          "col2_0",
          "col2_1",
          "col2_2",
          "col3",
          "col4_0",
          "col4_1",
      ]
      encoder = encoders.HelmertEncoder(
          handle_unknown="value", handle_missing="value"
      )
  
      encoder.fit(train)
      columns = encoder.transform(train).columns.to_numpy()
  
      self.assertTrue(np.array_equal(expected_columns, columns))
  
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 6 for calling the TestHelmertEncoder obj's underlying member method code with example usage: obj.test_helmert_2StringCols_ExpectCorrectOrder() without return types