code: def get_ego_node_num(graph, target_idx):
      G_ego = nx.ego_graph(graph, target_idx, radius=2)
      return G_ego.number_of_nodes()
  
file_path: stellargraph/tests/interpretability/test_saliency_maps_gat.py
imports: import pytest
  from stellargraph.interpretability.saliency_maps import IntegratedGradientsGAT
  import numpy
  from stellargraph.layer import GAT
  from stellargraph.mapper import FullBatchNodeGenerator
  from tensorflow.keras import Model
  from tensorflow.keras.optimizers import Adam
  from tensorflow.keras.losses import categorical_crossentropy
  import networkx
  from tensorflow.keras import backend
  from ..test_utils.graphs import example_graph_1_saliency_maps
label_desc: Use image node_id 2 for calling a global function with example usage: get_ego_node_num(graph, target_idx) and returns: G_ego