code: def test_number_of_isolates():
      G = nx.Graph()
      G.add_edge(0, 1)
      G.add_nodes_from([2, 3])
      assert nx.number_of_isolates(G) == 2
  
imports: import networkx
label_desc: Use image node_id 3 for calling a global function with example usage: test_number_of_isolates() without return types