code: def test_traverse_merge(self):
      x = [{"foo": 1, "bar": 2}, {"foo": 3, "bar": 4}]
      traversal_base = traverse_util.t_identity.each()
      traversal = traversal_base.merge(
          traverse_util.TraverseItem("foo"),
          traverse_util.TraverseItem("bar"),
      )
      self.assertEqual(list(traversal.iterate(x)), [1, 2, 3, 4])
      y = traversal.update(lambda x: x + x, x)
      self.assertEqual(y, [{"foo": 2, "bar": 4}, {"foo": 6, "bar": 8}])
  
imports: import collections
  import jax
  import jax.numpy
  import numpy
  import optax
  from absl.testing import absltest
  import flax
  from flax import traverse_util
  from flax.core import freeze
label_desc: Use image node_id 9 for calling the TraversalTest obj's underlying member method code with example usage: obj.test_traverse_merge() without return types