code: def test_nprobe_4(self):
      index = faiss.index_factory(32, "PCAR32,IVF32,SQ8,RFlat")
      ps = faiss.ParameterSpace()
  
      ps.set_index_parameter(index, "nprobe", 5)
      index2 = faiss.downcast_index(index.base_index)
      index2 = faiss.downcast_index(index2.index)
      self.assertEqual(index2.nprobe, 5)
  
file_path: faiss/tests/test_autotune.py
imports: import unittest
  import faiss
label_desc: Use image node_id 4 for calling the TestParameterSpace obj's underlying member method code with example usage: obj.test_nprobe_4() without return types