code: def test_signature(self):
      if hasattr(inspect, "signature"):
          sig = inspect.signature(doc.f1)
          self.assertEqual(str(sig), "(x)")
  
imports: from __future__ import absolute_import
  import sys
  import doctest
  import unittest
  import decimal
  import inspect
  import functools
  import collections
  from collections import defaultdict
  from decorator import dispatch_on, contextmanager, decorator
label_desc: Use image node_id 2 for calling the ExtraTestCase obj's underlying member method code with example usage: obj.test_signature() without return types