code: def test_gaps(self):
      gaps1_all = self.series1.gaps(mode="all")
      assert gaps1_all.empty
      gaps1_any = self.series1.gaps(mode="any")
      assert gaps1_any.empty
  
      gaps4_all = self.series4.gaps(mode="all")
      assert (
          gaps4_all["gap_start"]
          == pd.DatetimeIndex([pd.Timestamp("20130208")])
      ).all()
      assert (
          gaps4_all["gap_end"]
          == pd.DatetimeIndex([pd.Timestamp("20130208")])
      ).all()
      assert gaps4_all["gap_size"].values.tolist() == [1]
  
      gaps4_any = self.series4.gaps(mode="any")
      assert (
          gaps4_any["gap_start"]
          == pd.DatetimeIndex(
              [pd.Timestamp("20130208"), pd.Timestamp("20130211")]
          )
      ).all()
      assert (
          gaps4_any["gap_end"]
          == pd.DatetimeIndex(
              [pd.Timestamp("20130208"), pd.Timestamp("20130214")]
          )
      ).all()
      assert gaps4_any["gap_size"].values.tolist() == [1, 4]
  
imports: import numpy
  import pandas
  import pytest
  from darts import TimeSeries
  from darts.tests.test_timeseries import TestTimeSeries
label_desc: Use image node_id 21 for calling the TestTimeSeriesMultivariate obj's underlying member method code with example usage: obj.test_gaps() without return types