code: def test_add_holidays(self):
      times = pd.date_range(
          start=pd.Timestamp("20201201"), periods=30, freq="D"
      )
      seriesA = TimeSeries.from_times_and_values(
          times, range(len(times))
      )
  
      # testing for christmas and non-holiday in US
      seriesA = seriesA.add_holidays("US")
      last_column = seriesA.pd_dataframe().iloc[:, seriesA.width - 1]
      assert last_column.at[pd.Timestamp("20201225")] == 1
      assert last_column.at[pd.Timestamp("20201210")] == 0
      assert last_column.at[pd.Timestamp("20201226")] == 0
  
      # testing for christmas and non-holiday in PL
      seriesA = seriesA.add_holidays("PL")
      last_column = seriesA.pd_dataframe().iloc[:, seriesA.width - 1]
      assert last_column.at[pd.Timestamp("20201225")] == 1
      assert last_column.at[pd.Timestamp("20201210")] == 0
      assert last_column.at[pd.Timestamp("20201226")] == 1
      assert seriesA.width == 3
  
      # testing hourly time series
      times = pd.date_range(
          start=pd.Timestamp("20201224"), periods=50, freq="H"
      )
      seriesB = TimeSeries.from_times_and_values(
          times, range(len(times))
      )
      seriesB = seriesB.add_holidays("US")
      last_column = seriesB.pd_dataframe().iloc[:, seriesB.width - 1]
      assert last_column.at[pd.Timestamp("2020-12-25 01:00:00")] == 1
      assert last_column.at[pd.Timestamp("2020-12-24 23:00:00")] == 0
  
imports: import numpy
  import pandas
  import pytest
  from darts import TimeSeries
  from darts.tests.test_timeseries import TestTimeSeries
label_desc: Use image node_id 17 for calling the TestTimeSeriesMultivariate obj's underlying member method code with example usage: obj.test_add_holidays() without return types