code: def _test_ddp_sum(rank: int, worldsize: int = NUM_PROCESSES) -> None:
      dummy = DummyMetric()
      dummy._reductions = {"foo": torch.sum}
      dummy.foo = tensor(1)
      dummy._sync_dist()
  
      assert dummy.foo == worldsize
  
imports: import os
  import sys
  from copy import deepcopy
  from functools import partial
  import pytest
  import torch
  from torch import tensor
  from torchmetrics import Metric
  from torchmetrics.utilities.distributed import gather_all_tensors
  from torchmetrics.utilities.exceptions import TorchMetricsUserError
  from unittests import NUM_PROCESSES
  from unittests.helpers import seed_all
  from unittests.helpers.testers import DummyListMetric, DummyMetric, DummyMetricSum
label_desc: Use image node_id 1 for calling a global function with example usage: _test_ddp_sum(rank, worldsize) without return types