code: def test_build_lag_df_col_names_only():
      """Testing for the case where no df is passed and only col_names are generated."""
      lag_info = build_lag_df(
          value_col="x", df=None, max_order=3, orders=None
      )
  
      col_names = lag_info["col_names"]
  
      assert col_names == [
          "x_lag1",
          "x_lag2",
          "x_lag3",
      ], "The expected column names were not found in lags dataframe (lag_df)"
  
      assert lag_info["lag_df"] is None, "returned lag_df must be None"
  
imports: import numpy
  import pandas
  import pytest
  from greykite.common.features.timeseries_lags import build_agg_lag_df
  from greykite.common.features.timeseries_lags import build_autoreg_df
  from greykite.common.features.timeseries_lags import build_autoreg_df_multi
  from greykite.common.features.timeseries_lags import build_lag_df
  from greykite.common.features.timeseries_lags import min_max_lag_order
  from greykite.common.python_utils import assert_equal
label_desc: Use image node_id 3 for calling a global function with example usage: test_build_lag_df_col_names_only() without return types