code: def testInvalidScale(self):
      with self.assertRaisesOpError("`scale` must be positive"):
          normal_inverse_gaussian = nig.NormalInverseGaussian(
              loc=0.0,
              scale=-1.0,
              tailweight=2.0,
              skewness=1.0,
              validate_args=True,
          )
          self.evaluate(normal_inverse_gaussian.mean())
  
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 2 for calling the _NormalInverseGaussianTest obj's underlying member method code with example usage: obj.testInvalidScale() without return types