code: def test_get_item(self):
      f_map = FlatMap({"foo": {"b": [1], "d": {"e": 2}}, "bar": (1,)})
      self.assertEqual(f_map["foo"], {"b": [1], "d": {"e": 2}})
      self.assertEqual(f_map["bar"], (1,))
      with self.assertRaises(KeyError):
          _ = f_map["b"]
  
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 22 for calling the FlatMappingTest obj's underlying member method code with example usage: obj.test_get_item() without return types