code: def gis_shc():
      graph = nx.Graph()
      graph.add_nodes_from([1, 2, 3, 4])
      graph.add_edges_from([(1, 2), (2, 3), (3, 4)])
      return graph
  
imports: import itertools
  import pytest
  import networkx
label_desc: Use image node_id 16 for calling a global function with example usage: gis_shc() and returns: graph