code: def test_TimeSeriesDifferentiator_fit():
      """
      Test that TimeSeriesDifferentiator fit method returns self.
      """
      X = np.arange(10)
      tsd = TimeSeriesDifferentiator(order=1)
  
      assert tsd.fit(X) == tsd
  
imports: import re
  import pytest
  import numpy
  from skforecast.preprocessing import TimeSeriesDifferentiator
label_desc: Use image node_id 1 for calling a global function with example usage: test_TimeSeriesDifferentiator_fit() without return types