code: def testInvalidScale(self):
      scale = [-0.01, 0.0, 2.0]
      with self.assertRaisesOpError(
          "Argument `scale` must be positive."
      ):
          dist = moyal.Moyal(loc=0.0, scale=scale, validate_args=True)
          self.evaluate(dist.mean())
  
      scale = tf.Variable([0.01])
      self.evaluate(scale.initializer)
      dist = moyal.Moyal(loc=0.0, scale=scale, validate_args=True)
      self.assertIs(scale, dist.scale)
      self.evaluate(dist.mean())
      with tf.control_dependencies([scale.assign([-0.01])]):
          with self.assertRaisesOpError(
              "Argument `scale` must be positive."
          ):
              self.evaluate(dist.mean())
  
imports: import numpy
  from scipy import stats
  import tensorflow.compat.v1
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import kullback_leibler
  from tensorflow_probability.python.distributions import moyal
  from tensorflow_probability.python.internal import test_util
label_desc: Use image node_id 3 for calling the _MoyalTest obj's underlying member method code with example usage: obj.testInvalidScale() without return types