code: def test_pickle(self):
      import pickle
  
      dv = self.dv
      pdv = pickle.loads(pickle.dumps(dv, -1))
      assert dv._node == pdv._node
      assert dv._succ == pdv._succ
      assert dv._pred == pdv._pred
      assert dv.graph == pdv.graph
  
imports: import pytest
  import networkx
  from networkx.utils import edges_equal, nodes_equal
label_desc: Use image node_id 4 for calling the TestToDirected obj's underlying member method code with example usage: obj.test_pickle() without return types