code: def _random_tril_matrix(self, shape, seed):
      mat = tf.random.normal(shape=shape, seed=seed, dtype=self.dtype)
      chol = transform_diagonal.TransformDiagonal(
          shift.Shift(shift=self.dtype(1.0))(softplus.Softplus())
      )(mat)
      return tf.linalg.band_part(chol, -1, 0)
  
imports: from absl.testing import parameterized
  import numpy
  from scipy import stats
  import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import shift
  from tensorflow_probability.python.bijectors import softplus
  from tensorflow_probability.python.bijectors import transform_diagonal
  from tensorflow_probability.python.distributions import matrix_normal_linear_operator
  from tensorflow_probability.python.internal import test_util
label_desc: Use image node_id 1 for calling the _MatrixNormalTest obj's underlying member method code with example usage: obj._random_tril_matrix(shape, seed) and returns: tf