code: def test_list_to_packed(self):
      device = torch.device("cuda:0")
      N = 5
      K = 20
      x, x_dims = [], []
      dim2 = torch.randint(K, size=(1,)).item()
      for _ in range(N):
          dim1 = torch.randint(K, size=(1,)).item()
          x_dims.append(dim1)
          x.append(torch.rand([dim1, dim2], device=device))
  
      out = struct_utils.list_to_packed(x)
      x_packed = out[0]
      num_items = out[1]
      item_packed_first_idx = out[2]
      item_packed_to_list_idx = out[3]
  
      cur = 0
      for i in range(N):
          self.assertTrue(num_items[i] == x_dims[i])
          self.assertTrue(item_packed_first_idx[i] == cur)
          self.assertTrue(
              item_packed_to_list_idx[cur : cur + x_dims[i]].eq(i).all()
          )
          self.assertClose(x_packed[cur : cur + x_dims[i]], x[i])
          cur += x_dims[i]
  
file_path: pytorch3d/tests/test_struct_utils.py
imports: import unittest
  import torch
  from pytorch3d.structures import utils
  from .common_testing import TestCaseMixin
label_desc: Use image node_id 6 for calling the TestStructUtils obj's underlying member method code with example usage: obj.test_list_to_packed() without return types