code: def test_float(self):
      self._dll.tf_f.restype = c_float
      self._dll.tf_f.argtypes = (c_float,)
      self.assertEqual(self._dll.tf_f(-42.0), -14.0)
      self.assertEqual(self.S(), -42)
  
imports: import unittest
  from ctypes import *
  from ctypes.test import need_symbol
  import _ctypes_test
label_desc: Use image node_id 23 for calling the CFunctions obj's underlying member method code with example usage: obj.test_float() without return types