code: def test_pickle(self):
      import pickle
  
      uv = self.uv
      puv = pickle.loads(pickle.dumps(uv, -1))
      assert uv._node == puv._node
      assert uv._adj == puv._adj
      assert uv.graph == puv.graph
      assert hasattr(uv, "_graph")
  
imports: import pytest
  import networkx
  from networkx.utils import edges_equal, nodes_equal
label_desc: Use image node_id 4 for calling the TestToUndirected obj's underlying member method code with example usage: obj.test_pickle() without return types