code: def test_fill_constant(self):
      seriesA: TimeSeries = TimeSeries.from_times_and_values(
          self.time,
          np.array(
              [np.nan] * 5
              + [2.0] * 5
              + [np.nan] * 5
              + [2.0] * 10
              + [np.nan] * 5
          ),
      )
  
      # Check that no changes are made if there are no missing values
      assert self.series1 == fill_missing_values(self.series1, "auto")
  
      # Check that a constant function is filled to a constant function
      assert self.series1 == fill_missing_values(seriesA, "auto")
  
file_path: darts/darts/tests/utils/test_missing_values.py
imports: import numpy
  import pandas
  from darts import TimeSeries
  from darts.utils.missing_values import fill_missing_values, missing_values_ratio
label_desc: Use image node_id 1 for calling the TestMissingValues obj's underlying member method code with example usage: obj.test_fill_constant() without return types