class_docstr: ETH old benchmark with only 4 scenes
code: def __len__(self):
      return len(self.list_fragment)
  
imports: import gdown
  import os
  import os.path
  import logging
  import requests
  import glob
  import re
  import sys
  import csv
  from zipfile import ZipFile
  from torch_points3d.datasets.registration.basetest import BasePCRBTest
  from torch_points3d.datasets.base_dataset import BaseDataset
  from torch_points3d.datasets.registration.base_siamese_dataset import BaseSiameseDataset
  from torch_points3d.datasets.registration.basetest import Base3DMatchTest
  from torch_points3d.datasets.registration.base_siamese_dataset import GeneralFragment
  from torch_points3d.metrics.registration_tracker import FragmentRegistrationTracker
  from torch_points3d.datasets.registration.utils import files_exist
  from torch_points3d.datasets.registration.utils import makedirs
label_desc: Use image node_id 3 for calling the TestPairETH2 obj's underlying member method code with example usage: obj.__len__() and returns: len