code: def test_differencer_produces_expected_results(na_handling):
      """Test that Differencer produces expected results on a simple DataFrame."""
      transformer = Differencer(na_handling=na_handling)
      y_transformed = transformer.fit_transform(y_simple)
      y_expected = y_simple_expected_diff[na_handling]
  
      _assert_array_almost_equal(y_transformed, y_expected)
  
file_path: sktime/sktime/transformations/series/tests/test_differencer.py
imports: import numpy
  import pandas
  import pytest
  from sktime.datasets import load_airline
  from sktime.transformations.series.difference import Differencer
  from sktime.utils._testing.estimator_checks import _assert_array_almost_equal
  from sktime.utils.validation._dependencies import _check_soft_dependencies
label_desc: Use image node_id 1 for calling a global function with example usage: test_differencer_produces_expected_results(na_handling) without return types