code: def gis_hc():
      graph = nx.Graph()
      graph.add_nodes_from([1, 2, 3, 4, 5, 6])
      graph.add_edges_from([(1, 5), (2, 5), (3, 6), (4, 6), (5, 6)])
      return graph
  
imports: import itertools
  import pytest
  import networkx
label_desc: Use image node_id 17 for calling a global function with example usage: gis_hc() and returns: graph