code: def test_setbackend(self):
      sp3d.nn.set_backend("torchsparse")
      c = sp3d.nn.Conv3d(1, 1)
      sp3d.nn.set_backend("minkowski")
      self.assertNotIsInstance(sp3d.nn.Conv3d(1, 1), type(c))
      c = sp3d.nn.Conv3d(1, 1)
      sp3d.nn.set_backend("torchsparse")
      self.assertNotIsInstance(sp3d.nn.Conv3d(1, 1), type(c))
  
file_path: torch-points3d/test/test_sparseconv.py
imports: import os
  import sys
  import unittest
  import torch_points3d.modules.SparseConv3d
  import torch_points3d.modules.SparseConv3d.modules
label_desc: Use image node_id 1 for calling the TestSparseConv obj's underlying member method code with example usage: obj.test_setbackend() without return types