class_docstr: Base class for the reference tests.
code: def test_return_possibly_undefined_illegal(self, n):
      with self.assertRaisesRegex(
          ValueError, "else branch must also have a return"
      ):
          tf.function(return_possibly_undefined)(tf.constant(n))
  
imports: import itertools
  from absl.testing import parameterized
  import tensorflow
  from tensorflow.python.autograph.tests import reference_test_base
label_desc: Use image node_id 4 for calling the ReferenceTest obj's underlying member method code with example usage: obj.test_return_possibly_undefined_illegal(n) without return types