code: def testVariableGradients(self):
      loc = tf.Variable([1.0, 2.0])
      dist = det.VectorDeterministic(loc=loc, validate_args=True)
      with tf.GradientTape() as tape:
          s = dist.sample(seed=test_util.test_seed())
      g = tape.gradient(s, dist.trainable_variables)
      self.assertLen(g, 1)
      self.assertAllNotNone(g)
  
imports: from absl.testing import parameterized
  import numpy
  import tensorflow.compat.v1
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import deterministic
  from tensorflow_probability.python.distributions import gamma
  from tensorflow_probability.python.distributions import kullback_leibler
  from tensorflow_probability.python.distributions import mvn_diag
  from tensorflow_probability.python.internal import tensorshape_util
  from tensorflow_probability.python.internal import test_util
label_desc: Use image node_id 19 for calling the VectorDeterministicTest obj's underlying member method code with example usage: obj.testVariableGradients() without return types