code: def test_true_streaming_covariance(self):
      fake_kernel = test_fixtures.TestTransitionKernel(())
      cov_reducer = covariance_reducer.CovarianceReducer()
      reduction_rslt, _, _ = sample_fold(
          num_steps=20,
          current_state=tf.convert_to_tensor([0.0, 0.0]),
          kernel=fake_kernel,
          reducer=cov_reducer,
          seed=test_util.test_seed(),
      )
      reduction_rslt = self.evaluate(reduction_rslt)
      self.assertAllClose(
          np.cov(
              np.column_stack((np.arange(20), np.arange(20))).T, ddof=0
          ),
          reduction_rslt,
          rtol=1e-5,
      )
  
imports: import collections
  import warnings
  from absl.testing import parameterized
  import numpy
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import normal
  from tensorflow_probability.python.experimental.mcmc import covariance_reducer
  from tensorflow_probability.python.experimental.mcmc import expectations_reducer
  from tensorflow_probability.python.experimental.mcmc.internal import test_fixtures
  from tensorflow_probability.python.experimental.mcmc.sample_fold import sample_chain_with_burnin
  from tensorflow_probability.python.experimental.mcmc.sample_fold import sample_fold
  from tensorflow_probability.python.internal import samplers
  from tensorflow_probability.python.internal import tensorshape_util
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.mcmc import hmc
label_desc: Use image node_id 6 for calling the SampleFoldTest obj's underlying member method code with example usage: obj.test_true_streaming_covariance() without return types