code: def test_traverse_filter(self):
      x = [1, -2, 3, -4]
      traversal = traverse_util.t_identity.each().filter(
          lambda x: x < 0
      )
      self.assertEqual(list(traversal.iterate(x)), [-2, -4])
      y = traversal.update(lambda x: -x, x)
      self.assertEqual(y, [1, 2, 3, 4])
  
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 13 for calling the TraversalTest obj's underlying member method code with example usage: obj.test_traverse_filter() without return types