code: def test_factory(self):
      import faiss
  
      index = FaissIndex(string_factory="Flat")
      index.add_vectors(np.eye(5, dtype=np.float32))
      self.assertIsInstance(index.faiss_index, faiss.IndexFlat)
      index = FaissIndex(string_factory="LSH")
      index.add_vectors(np.eye(5, dtype=np.float32))
      self.assertIsInstance(index.faiss_index, faiss.IndexLSH)
      with self.assertRaises(ValueError):
          _ = FaissIndex(
              string_factory="Flat", custom_index=faiss.IndexFlat(5)
          )
  
imports: import os
  import tempfile
  from functools import partial
  from unittest import TestCase
  from unittest.mock import patch
  import numpy
  import pytest
  from datasets.arrow_dataset import Dataset
  from datasets.search import ElasticSearchIndex, FaissIndex, MissingIndex
  from .utils import require_elasticsearch, require_faiss
label_desc: Use image node_id 2 for calling the FaissIndexTest obj's underlying member method code with example usage: obj.test_factory() without return types