code: def test_bfs_tree_isolates(self):
      G = nx.Graph()
      G.add_node(1)
      G.add_node(2)
      T = nx.bfs_tree(G, source=1)
      assert sorted(T.nodes()) == [1]
      assert sorted(T.edges()) == []
  
imports: from functools import partial
  import pytest
  import networkx
label_desc: Use image node_id 8 for calling the TestBFS obj's underlying member method code with example usage: obj.test_bfs_tree_isolates() without return types