code: def test_const_impute_timeseries_dataframe(self):
      data = {"data": [np.nan, 1, np.nan, 2, 3]}
      df = pd.DataFrame(data)
      res_df = _const_impute_timeseries_dataframe(df, 1)
      assert res_df["data"][0] == 1
      assert res_df["data"][2] == 1
  
file_path: BigDL/python/chronos/test/bigdl/chronos/data/utils/test_impute.py
imports: import pytest
  import pandas
  import numpy
  from unittest import TestCase
  from bigdl.chronos.data.utils.impute import impute_timeseries_dataframe, _last_impute_timeseries_dataframe, _const_impute_timeseries_dataframe, _linear_impute_timeseries_dataframe
  from ...None import op_torch, op_tf2
label_desc: Use image node_id 5 for calling the TestImputeTimeSeries obj's underlying member method code with example usage: obj.test_const_impute_timeseries_dataframe() without return types