code: def testAssertValidSample(self):
      d = half_normal.HalfNormal(scale=[2.0, 3.0], validate_args=True)
      with self.assertRaisesOpError("Sample must be non-negative."):
          d.log_prob(-0.2)
  
imports: 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 half_normal
  from tensorflow_probability.python.distributions import kullback_leibler
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.math import gradient
label_desc: Use image node_id 21 for calling the HalfNormalTest obj's underlying member method code with example usage: obj.testAssertValidSample() without return types