code: def test_identity(self):
      # Test that an additive SSM with a single component defines the same
      # distribution as the component model.
  
      y = self._build_placeholder([1.0, 2.5, 4.3, 6.1, 7.8])
  
      local_ssm = LocalLinearTrendStateSpaceModel(
          num_timesteps=5,
          level_scale=0.3,
          slope_scale=0.6,
          observation_noise_scale=0.1,
          initial_state_prior=mvn_diag.MultivariateNormalDiag(
              scale_diag=self._build_placeholder([1.0, 1.0])
          ),
      )
  
      additive_ssm = AdditiveStateSpaceModel([local_ssm])
  
      local_lp = local_ssm.log_prob(y[:, np.newaxis])
      additive_lp = additive_ssm.log_prob(y[:, np.newaxis])
      self.assertAllClose(
          self.evaluate(local_lp), self.evaluate(additive_lp)
      )
  
imports: from absl.testing import parameterized
  import numpy
  import tensorflow.compat.v1
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import linear_gaussian_ssm
  from tensorflow_probability.python.distributions import mvn_diag
  from tensorflow_probability.python.internal import tensorshape_util
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.sts.components.local_linear_trend import LocalLinearTrendStateSpaceModel
  from tensorflow_probability.python.sts.components.sum import AdditiveStateSpaceModel
label_desc: Use image node_id 1 for calling the _AdditiveStateSpaceModelTest obj's underlying member method code with example usage: obj.test_identity() without return types