code: def forward(self, x, edge_index):
      return x
  
file_path: pytorch_geometric/test/explain/metric/test_fidelity.py
imports: import pytest
  import torch
  from torch_geometric.explain import DummyExplainer, Explainer, characterization_score, fidelity, fidelity_curve_auc
label_desc: Use image node_id 1 for calling the DummyModel obj's underlying member method code with example usage: obj.forward(x, edge_index) and returns: x