code: def testDoubleWhere(self):
      loc = 0.0
  
      def f(x):
          return nig.NormalInverseGaussian(
              loc=x, scale=2.0, tailweight=1.0, skewness=2.0
          ).log_prob(loc)
  
      _, g = gradient.value_and_gradient(f, loc)
      self.assertAllNotNan(g)
  
imports: import numpy
  from scipy import stats
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import normal_inverse_gaussian
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.math import gradient
label_desc: Use image node_id 13 for calling the _NormalInverseGaussianTest obj's underlying member method code with example usage: obj.testDoubleWhere() and returns: nig