code: def testUnderlyingDataSeries(self):
      ds = dataseries.SequenceDataSeries()
      testFilter = TestFilter(ds)
      for i in range(10):
          ds.append(i)
          ds.append(None)
  
      self.assertEqual(testFilter.getDataSeries(), ds)
      for i in range(0, len(testFilter)):
          self.assertEqual(testFilter[i], ds[i])
          self.assertEqual(testFilter.getDataSeries()[i], ds[i])
  
file_path: pyalgotrade/testcases/technical_test.py
imports: from .None import common
  from pyalgotrade import technical
  from pyalgotrade import dataseries
label_desc: Use image node_id 2 for calling the DataSeriesFilterTest obj's underlying member method code with example usage: obj.testUnderlyingDataSeries() without return types