code: def testAssertsValidSample(self):
      g = gamma_lib.Gamma(
          concentration=2.0, rate=3.0, validate_args=True
      )
      with self.assertRaisesOpError("Sample must be non-negative."):
          self.evaluate(g.log_prob(-0.1))
  
imports: import functools
  from absl.testing import parameterized
  import numpy
  from scipy import misc
  from scipy import special
  from scipy import stats
  import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import exp
  from tensorflow_probability.python.distributions import gamma
  from tensorflow_probability.python.distributions import kullback_leibler
  from tensorflow_probability.python.distributions.internal import statistical_testing
  from tensorflow_probability.python.internal import implementation_selection
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.math import gradient
label_desc: Use image node_id 4 for calling the GammaTest obj's underlying member method code with example usage: obj.testAssertsValidSample() without return types