code: def test_segment_sum_optional_num_segments(self):
      result = utils.segment_sum(
          jnp.arange(9), jnp.array([0, 1, 2, 0, 4, 0, 1, 1, 0])
      )
      np.testing.assert_allclose(result, jnp.array([16, 14, 2, 0, 4]))
  
imports: import functools
  import os
  from absl.testing import absltest
  from absl.testing import parameterized
  import jax
  from jax.lib import xla_bridge
  import jax.numpy
  import jax.tree_util
  from jraph._src import graph
  from jraph._src import utils
  import numpy
label_desc: Use image node_id 17 for calling the GraphTest obj's underlying member method code with example usage: obj.test_segment_sum_optional_num_segments() without return types