code: def testHalfNormalShapeWithPlaceholders(self):
      if tf.executing_eagerly():
          return
      scale = tf1.placeholder_with_default([1.0, 2], shape=None)
      halfnorm = half_normal.HalfNormal(scale=scale, validate_args=True)
  
      # get_batch_shape should return an '<unknown>' tensor.
      self.assertEqual(halfnorm.batch_shape, tf.TensorShape(None))
      self.assertEqual(halfnorm.event_shape, ())
      self.assertAllEqual(
          self.evaluate(halfnorm.event_shape_tensor()), []
      )
      self.assertAllEqual(
          self.evaluate(halfnorm.batch_shape_tensor()), [2]
      )
  
imports: from absl.testing import parameterized
  import numpy
  from scipy import stats
  import tensorflow.compat.v1
  import tensorflow.compat.v2
  from tensorflow_probability.python.distributions import half_normal
  from tensorflow_probability.python.distributions import kullback_leibler
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.math import gradient
label_desc: Use image node_id 25 for calling the HalfNormalTest obj's underlying member method code with example usage: obj.testHalfNormalShapeWithPlaceholders() without return types