code: def test_default_stream_cpu(self):
      stream = default_stream(torch.device("cpu"))
      assert stream is CPUStream
  
imports: import pytest
  import torch
  from fairscale.nn.pipe.stream import CPUStream, current_stream, default_stream, get_device, is_cuda, new_stream, record_stream, use_device, use_stream, wait_stream
label_desc: Use image node_id 1 for calling the TestDefaultStream obj's underlying member method code with example usage: obj.test_default_stream_cpu() without return types