code: def test_invalid_signs(self):
      with self.assertRaises(ValueError):
          int("+")
      with self.assertRaises(ValueError):
          int("-")
      with self.assertRaises(ValueError):
          int("- 1")
      with self.assertRaises(ValueError):
          int("+ 1")
      with self.assertRaises(ValueError):
          int(" + 1 ")
  
imports: import sys
  import time
  import unittest
  from unittest import mock
  from test import support
  from test.test_grammar import VALID_UNDERSCORE_LITERALS, INVALID_UNDERSCORE_LITERALS
label_desc: Use image node_id 2 for calling the IntTestCases obj's underlying member method code with example usage: obj.test_invalid_signs() without return types