code: def test_factory(self):
      AQ = faiss.AdditiveQuantizer
      ns, Msub, nbits = 2, 4, 8
      index = faiss.index_factory(64, f"PLSQ{ns}x{Msub}x{nbits}_Nqint8")
      assert isinstance(index, faiss.IndexProductLocalSearchQuantizer)
      self.assertEqual(index.plsq.nsplits, ns)
      self.assertEqual(index.plsq.subquantizer(0).M, Msub)
      self.assertEqual(index.plsq.subquantizer(0).nbits.at(0), nbits)
      self.assertEqual(index.plsq.search_type, AQ.ST_norm_qint8)
  
      code_size = (ns * Msub * nbits + 7) // 8 + 1
      self.assertEqual(index.plsq.code_size, code_size)
  
imports: import numpy
  import faiss
  import unittest
  from faiss.contrib import datasets
label_desc: Use image node_id 4 for calling the TestIndexProductLocalSearchQuantizer obj's underlying member method code with example usage: obj.test_factory() without return types