code: def _get_stream(self, stream_name):
      if stream_name == "null":
          return cuda.Stream.null
      elif stream_name == "ptds":
          return cuda.Stream.ptds
      else:
          return cuda.Stream()
  
imports: import unittest
  import pytest
  import cupy
  from cupy import cuda
  from cupy import testing
label_desc: Use image node_id 3 for calling the TestNewDLPackConversion obj's underlying member method code with example usage: obj._get_stream(stream_name) and returns: cuda, cuda, cuda