docstr: When `mean_reversion` is zero `zeta` returns `t`.
docstr_tok: ["When","`","mean_reversion","`","is","zero","`","zeta","`","returns","`","t","`","."]
code: def test_sample_paths_mean_reversion_is_zero(self):
      """When `mean_reversion` is zero `zeta` returns `t`."""
      # Construct CIR model
      (
          theta,
          _,
          sigma,
          initial_state,
          num_samples,
          times,
          random_type,
          seed,
          dtype,
      ) = self.get_default_params()
      mean_reversion = 0.0
      process = tff.models.cir.CirModel(
          theta=theta,
          mean_reversion=mean_reversion,
          sigma=sigma,
          dtype=dtype,
      )
      # Act
      samples = process.sample_paths(
          times=times,
          initial_state=initial_state,
          num_samples=num_samples,
          random_type=random_type,
          seed=seed,
      )
      # Assert
      with self.subTest("dType"):
          self.assertDTypeEqual(samples, dtype)
      with self.subTest("GreaterEqualThanZero"):
          self.assertAllGreaterEqual(samples, 0.0)
  
imports: from absl.testing import parameterized
  import numpy
  import tensorflow.compat.v2
  import tf_quant_finance
  from tensorflow.python.framework import test_util
  from tf_quant_finance.math import random_ops
label_desc: Use image node_id 9 for calling the CirTest obj's underlying member method code with example usage: obj.test_sample_paths_mean_reversion_is_zero() without return types