code: def test_TimeSeriesDifferentiator_fit_transform(order, expected):
      """
      Test TimeSeriesDifferentiator fit_transform method.
      """
      transformer = TimeSeriesDifferentiator(order=order)
      results = transformer.fit_transform(y)
  
      np.testing.assert_array_equal(results, expected)
  
imports: import re
  import pytest
  import numpy
  from skforecast.preprocessing import TimeSeriesDifferentiator
label_desc: Use image node_id 2 for calling a global function with example usage: test_TimeSeriesDifferentiator_fit_transform(order, expected) without return types