code: def test_pickle_roundtrip(self, pickler):
      x = FlatMap({})
      y = pickler.loads(pickler.dumps(x))
      self.assertType(y, dict)
  
imports: import collections
  import copy
  import pickle
  import threading
  from absl.testing import absltest
  from absl.testing import parameterized
  import cloudpickle
  import dill
  from haiku._src import data_structures
  import jax
  import tree
label_desc: Use image node_id 12 for calling the FlatMappingTest obj's underlying member method code with example usage: obj.test_pickle_roundtrip(pickler) without return types