code: def test_forest_str_errors():
      ugraph = nx.complete_graph(3, create_using=nx.Graph)
  
      with pytest.raises(nx.NetworkXNotImplemented):
          nx.forest_str(ugraph)
  
      dgraph = nx.complete_graph(3, create_using=nx.DiGraph)
  
      with pytest.raises(nx.NetworkXNotImplemented):
          nx.forest_str(dgraph)
  
imports: import random
  from itertools import product
  from textwrap import dedent
  import pytest
  import networkx
label_desc: Use image node_id 7 for calling a global function with example usage: test_forest_str_errors() without return types