code: def __str__(self):
      s = ""
  
      if self.skipped:
          s += SubtestInfo.skipped_prefix
  
      return s + TEST_SUBTEST_SEPARATOR.join([self.test, self.subtest])
  
imports: import collections
  import functools
  import math
  import os
  import re
  import sys
  import yatest_lib.tools
label_desc: Use image node_id 3 for calling the SubtestInfo obj's underlying member method code with example usage: obj.__str__() and returns: unknown