code: def test_sum_of_white_noise_is_random_walk(self):
      num_timesteps = 20
      level_scale = 0.6
      noise_scale = 0.3
      random_walk_ssm = (
          linear_gaussian_ssm.LinearGaussianStateSpaceModel(
              num_timesteps=num_timesteps,
              transition_matrix=[[1.0]],
              transition_noise=mvn_diag.MultivariateNormalDiag(
                  loc=[0.0], scale_diag=[level_scale]
              ),
              observation_matrix=[[1.0]],
              observation_noise=mvn_diag.MultivariateNormalDiag(
                  loc=[0.0], scale_diag=[noise_scale]
              ),
              initial_state_prior=mvn_diag.MultivariateNormalDiag(
                  loc=[0.0], scale_diag=[level_scale]
              ),
          )
      )
  
      white_noise_ssm = (
          linear_gaussian_ssm.LinearGaussianStateSpaceModel(
              num_timesteps=num_timesteps,
              transition_matrix=[[0.0]],
              transition_noise=mvn_diag.MultivariateNormalDiag(
                  loc=[0.0], scale_diag=[level_scale]
              ),
              observation_matrix=[[1.0]],
              observation_noise=mvn_diag.MultivariateNormalDiag(
                  loc=[0.0], scale_diag=[noise_scale]
              ),
              initial_state_prior=mvn_diag.MultivariateNormalDiag(
                  loc=[0.0], scale_diag=[level_scale]
              ),
          )
      )
      cumsum_white_noise_ssm = IntegratedStateSpaceModel(
          white_noise_ssm
      )
      x, lp = cumsum_white_noise_ssm.experimental_sample_and_log_prob(
          [3], seed=test_util.test_seed()
      )
      self.assertAllClose(lp, random_walk_ssm.log_prob(x), atol=1e-5)
  
file_path: probability/tensorflow_probability/python/sts/components/autoregressive_integrated_moving_average_test.py
imports: import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import chain
  from tensorflow_probability.python.bijectors import cumsum
  from tensorflow_probability.python.bijectors import invert
  from tensorflow_probability.python.bijectors import reshape
  from tensorflow_probability.python.distributions import linear_gaussian_ssm
  from tensorflow_probability.python.distributions import mvn_diag
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.sts.components.autoregressive_integrated_moving_average import AutoregressiveMovingAverageStateSpaceModel
  from tensorflow_probability.python.sts.components.autoregressive_integrated_moving_average import IntegratedStateSpaceModel
label_desc: Use image node_id 1 for calling the IntegratedStateSpaceModelTest obj's underlying member method code with example usage: obj.test_sum_of_white_noise_is_random_walk() without return types