code: def test_deepcopy_still_immutable(self):
      before = FlatMap(dict(a=[1, 2, 3]))
      after = copy.deepcopy(before)
      with self.assertRaises(TypeError):
          before["a"] = [
              3,
              2,
              1,
          ]  # pytype: disable=unsupported-operands
      self.assertEqual(before["a"], [1, 2, 3])
      self.assertEqual(after["a"], [1, 2, 3])
  
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 19 for calling the FlatMappingTest obj's underlying member method code with example usage: obj.test_deepcopy_still_immutable() without return types