code: def test_fillzero(self):
      data = [[np.nan, 1], [np.nan, 2]]
      df = pd.DataFrame(data)
      imputor = FillZeroImpute()
      imputed_df = imputor.impute(df)
      assert df.isna().sum().sum() != 0
      assert imputed_df.isna().sum().sum() == 0
  
file_path: analytics-zoo/pyzoo/test/zoo/chronos/autots/deprecated/preprocessing/test_fill.py
imports: import numpy
  import pandas
  import pytest
  from test.zoo.pipeline.utils.test_utils import ZooTestCase
  from zoo.chronos.autots.deprecated.feature.time_sequence import TimeSequenceFeatureTransformer
  from zoo.chronos.autots.deprecated.preprocessing.impute.LastFill import LastFill
  from zoo.chronos.autots.deprecated.preprocessing.impute import FillZeroImpute
label_desc: Use image node_id 5 for calling the TestDataImputation obj's underlying member method code with example usage: obj.test_fillzero() without return types