code: def _test_mapping_file_plain(self):
      def unichrs(s):
          return "".join(chr(int(x, 16)) for x in s.split("+"))
  
      urt_wa = {}
  
      with self.open_mapping_file() as f:
          for line in f:
              if not line:
                  break
              data = line.split("#")[0].split()
              if len(data) != 2:
                  continue
  
              if data[0][:2] != "0x":
                  self.fail(f"Invalid line: {line!r}")
              csetch = bytes.fromhex(data[0][2:])
              if len(csetch) == 1 and 0x80 <= csetch[0]:
                  continue
  
              unich = unichrs(data[1])
              if ord(unich) == 0xFFFD or unich in urt_wa:
                  continue
              urt_wa[unich] = csetch
  
              self._testpoint(csetch, unich)
  
imports: import codecs
  import os
  import re
  import sys
  import unittest
  from http.client import HTTPException
  from test import support
  from io import BytesIO
label_desc: Use image node_id 4 for calling the TestBase_Mapping obj's underlying member method code with example usage: obj._test_mapping_file_plain() and returns: str