code: def test_no_copy_no_portal():
      skip_layout = SkipLayout(
          num_partitions=2,
          skip_routes={
              (None, "copy"): (0, 1),
              (None, "not_copy"): (0, 0),
          },
      )
      skip_tracker = SkipTrackerThroughPotals(skip_layout)
  
      batch = Batch(torch.tensor([1.0]))
      a = torch.tensor([2.0])
      b = torch.tensor([2.0])
  
      skip_tracker.save(batch, None, "copy", a)
      skip_tracker.save(batch, None, "not_copy", b)
  
      assert (None, "copy") in skip_tracker.portals
      assert (None, "copy") not in skip_tracker.tensors
      assert (None, "not_copy") in skip_tracker.tensors
      assert (None, "not_copy") not in skip_tracker.portals
  
file_path: pytorch/test/distributed/pipeline/sync/skip/test_tracker.py
imports: from queue import Queue
  import threading
  import pytest
  import torch
  from torch import nn
  from torch.distributed.pipeline.sync.checkpoint import enable_checkpointing, enable_recomputing
  from torch.distributed.pipeline.sync.microbatch import Batch
  from torch.distributed.pipeline.sync.skip import pop, skippable, stash
  from torch.distributed.pipeline.sync.skip.layout import SkipLayout
  from torch.distributed.pipeline.sync.skip.tracker import SkipTracker, SkipTrackerThroughPotals, current_skip_tracker
  from torch.testing._internal.common_utils import run_tests
label_desc: Use image node_id 4 for calling a global function with example usage: test_no_copy_no_portal() without return types