code: def _test_allreduce(self, backend):
      store = c10d.FileStore(self.file_name, self.world_size)
      # This is required because these functions calls directly to the .dist and needs
      # the world to be initialized
      c10d.init_process_group(
          store=store,
          rank=self.rank,
          world_size=self.world_size,
          backend=backend,
      )
      device = torch.device(f"cuda:{self.rank}")
      x = torch.ones(5, 5, device=device) + self.rank
      x.requires_grad = True
      y = torch.distributed.nn.all_reduce(x, op=c10d.ReduceOp.SUM)
  
      self.assertEqual(y, 3 * torch.ones(5, 5, device=device))
  
      z = y.sin().sum()
      z.backward()
      x_g = 2 * (3 * torch.ones(5, 5, device=device)).cos()
      self.assertEqual(x.grad, x_g)
  
imports: import os
  import sys
  import tempfile
  import torch
  import torch.distributed
  import torch.multiprocessing
  from torch.testing._internal.common_distributed import MultiProcessTestCase
  from torch.testing._internal.common_utils import load_tests, NO_MULTIPROCESSING_SPAWN
label_desc: Use image node_id 7 for calling the TestDistributedNNFunctions obj's underlying member method code with example usage: obj._test_allreduce(backend) without return types