code: def test_when_covariates_are_present_then_covariates_are_preserved():
      original_df = DATAFRAME_WITH_COVARIATES.copy()
      original_columns = original_df.columns
      splitter = ExpandingWindowSplitter(
          prediction_length=3, num_val_windows=2
      )
  
      for train_fold, val_fold in splitter.split(original_df):
          assert train_fold.columns.equals(original_columns)
          assert val_fold.columns.equals(original_columns)
  
file_path: autogluon/timeseries/tests/unittests/test_splitter.py
imports: import pytest
  from autogluon.timeseries.splitter import ExpandingWindowSplitter
  from .common import DATAFRAME_WITH_COVARIATES, DATAFRAME_WITH_STATIC, DUMMY_VARIABLE_LENGTH_TS_DATAFRAME
label_desc: Use image node_id 4 for calling a global function with example usage: test_when_covariates_are_present_then_covariates_are_preserved() without return types