code: def _get_simple_implicit_function(self, scaffold_res=16):
      default_cfg = get_default_args(VoxelGridImplicitFunction)
      custom_cfg = DictConfig(
          {
              "voxel_grid_density_args": {
                  "voxel_grid_FullResolutionVoxelGrid_args": {
                      "n_features": 7
                  }
              },
              "decoder_density_class_type": "ElementwiseDecoder",
              "decoder_color_class_type": "MLPDecoder",
              "decoder_color_MLPDecoder_args": {
                  "network_args": {
                      "n_layers": 2,
                      "output_dim": 3,
                      "hidden_dim": 128,
                  }
              },
              "scaffold_resolution": (
                  scaffold_res,
                  scaffold_res,
                  scaffold_res,
              ),
          }
      )
      cfg = OmegaConf.merge(default_cfg, custom_cfg)
      return VoxelGridImplicitFunction(**cfg)
  
file_path: pytorch3d/tests/implicitron/test_voxel_grid_implicit_function.py
imports: import unittest
  import torch
  from omegaconf import DictConfig, OmegaConf
  from pytorch3d.implicitron.models.implicit_function.voxel_grid_implicit_function import VoxelGridImplicitFunction
  from pytorch3d.implicitron.models.renderer.base import ImplicitronRayBundle
  from pytorch3d.implicitron.tools.config import expand_args_fields, get_default_args
  from pytorch3d.renderer import ray_bundle_to_ray_points
  from tests.common_testing import TestCaseMixin
label_desc: Use image node_id 2 for calling the TestVoxelGridImplicitFunction obj's underlying member method code with example usage: obj._get_simple_implicit_function(scaffold_res) and returns: VoxelGridImplicitFunction