code: def forward(
      self, x_dict, edge_index_dict, additonal_arg=None
  ) -> torch.Tensor:
      return self.lin(self.graph_sage(x_dict, edge_index_dict)["paper"])
  
file_path: pytorch_geometric/test/explain/conftest.py
imports: from typing import Optional
  import pytest
  import torch
  from torch_geometric.data import Data, HeteroData
  from torch_geometric.explain import Explanation
  from torch_geometric.explain.config import MaskType
  from torch_geometric.nn import SAGEConv, to_hetero
  from torch_geometric.testing import get_random_edge_index
label_desc: Use image node_id 2 for calling the HeteroSAGE obj's underlying member method code with example usage: obj.forward(x_dict, edge_index_dict, additonal_arg) and returns: self