code: def test_buf_read(self):
      x = np.random.uniform(size=20)
  
      fd, fname = tempfile.mkstemp()
      os.close(fd)
      try:
          x.tofile(fname)
  
          with open(fname, "rb") as f:
              reader = faiss.PyCallbackIOReader(f.read, 1234)
  
              bsz = 123
              reader = faiss.BufferedIOReader(reader, bsz)
  
              y = np.zeros_like(x)
              print("nbytes=", y.nbytes)
              reader(faiss.swig_ptr(y), y.nbytes, 1)
  
          np.testing.assert_array_equal(x, y)
      finally:
          if os.path.exists(fname):
              os.unlink(fname)
  
imports: import numpy
  import unittest
  import faiss
  import tempfile
  import os
  import io
  import sys
  import pickle
  from multiprocessing.pool import ThreadPool
label_desc: Use image node_id 2 for calling the TestCallbacks obj's underlying member method code with example usage: obj.test_buf_read() without return types