code: def _random_tril_matrix(self, shape):
      mat = self.rng.rand(*shape)
      chol = transform_diagonal.TransformDiagonal(softplus.Softplus())(
          mat
      )
      return tf.linalg.band_part(chol, -1, 0)
  
imports: import numpy
  from scipy import stats
  import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import softplus
  from tensorflow_probability.python.bijectors import transform_diagonal
  from tensorflow_probability.python.distributions import kullback_leibler
  from tensorflow_probability.python.distributions import mvn_linear_operator
  from tensorflow_probability.python.internal import tensorshape_util
  from tensorflow_probability.python.internal import test_util
label_desc: Use image node_id 2 for calling the MultivariateNormalLinearOperatorTest obj's underlying member method code with example usage: obj._random_tril_matrix(shape) and returns: tf