code: def test_custom_pytree(self):
      def f():
          init = lambda: None
          foo = lambda: "foo"
          bar = lambda: "bar"
          return init, AttrMap(foo=foo, bar=bar)
  
      f = multi_transform.multi_transform(f)
      self.assertEqual("foo", f.apply.foo({}, None))
      self.assertEqual("bar", f.apply.bar({}, None))
  
imports: import inspect
  from typing import Optional, Union
  from absl.testing import absltest
  from absl.testing import parameterized
  from haiku._src import base
  from haiku._src import multi_transform
  from haiku._src import transform
  from haiku._src import typing
  import jax
  import jax.numpy
  import numpy
label_desc: Use image node_id 2 for calling the MultiTransformTest obj's underlying member method code with example usage: obj.test_custom_pytree() and returns: init,  AttrMap