code: def test_forecaster_index_step_stored():
      """
      Test serie without DatetimeIndex, step is stored in forecaster.index_freq.
      """
      y = pd.Series(data=np.arange(10))
      forecaster = ForecasterAutoregDirect(
          LinearRegression(), lags=3, steps=2
      )
      forecaster.fit(y=y)
      expected = y.index.step
      results = forecaster.index_freq
  
      assert results == expected
  
file_path: skforecast/skforecast/ForecasterAutoregDirect/tests/test_fit.py
imports: import re
  import pytest
  import numpy
  import pandas
  from skforecast.ForecasterAutoregDirect import ForecasterAutoregDirect
  from sklearn.linear_model import LinearRegression
label_desc: Use image node_id 2 for calling a global function with example usage: test_forecaster_index_step_stored() without return types