code: def testNegativeSigmaFails(self):
      with self.assertRaisesOpError("`scale` must be positive"):
          dist = truncated_normal.TruncatedNormal(
              loc=0.0,
              scale=-0.1,
              low=-1.0,
              high=1.0,
              validate_args=True,
          )
          self.evaluate(dist.mean())
  
imports: import itertools
  import unittest
  from absl.testing import parameterized
  import numpy
  from scipy import stats
  import tensorflow.compat.v1
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import normal
  from tensorflow_probability.python.distributions import truncated_normal
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.math import gradient
label_desc: Use image node_id 7 for calling the TruncatedNormalStandaloneTestCase obj's underlying member method code with example usage: obj.testNegativeSigmaFails() without return types