code: def test_merge_different_mappings(self):
      a = collections.defaultdict(dict)
      a["foo"]["bar"] = 1
      b = {"foo": {"baz": 2}}
      c = types.MappingProxyType({"foo": {"bat": 3}})
      d = filtering.merge(a, b, c)
      self.assertEqual(d, {"foo": {"bar": 1, "baz": 2, "bat": 3}})
  
imports: import collections
  from collections.abc import Sequence
  import itertools
  import re
  import types
  from typing import Any, Callable
  from absl.testing import absltest
  from absl.testing import parameterized
  from haiku._src import basic
  from haiku._src import data_structures
  from haiku._src import filtering
  from haiku._src import transform
  import jax
  import jax.numpy
label_desc: Use image node_id 13 for calling the FilteringTest obj's underlying member method code with example usage: obj.test_merge_different_mappings() without return types