    def _test_mapping_file_plain(self):
        unichrs = lambda s: ''.join(map(chr, map(eval, s.split('+'))))
        urt_wa = {}

        with self.open_mapping_file() as f:
            for line in f:
                if not line:
                    break
                data = line.split('#')[0].strip().split()
                if len(data) != 2:
                    continue

                csetval = eval(data[0])
                if csetval <= 0x7F:
                    csetch = bytes([csetval & 0xff])
                elif csetval >= 0x1000000:
                    csetch = bytes([(csetval >> 24), ((csetval >> 16) & 0xff),
                                    ((csetval >> 8) & 0xff), (csetval & 0xff)])
                elif csetval >= 0x10000:
                    csetch = bytes([(csetval >> 16), ((csetval >> 8) & 0xff),
                                    (csetval & 0xff)])
                elif csetval >= 0x100:
                    csetch = bytes([(csetval >> 8), (csetval & 0xff)])
                else:
                    continue

                unich = unichrs(data[1])
                if ord(unich) == 0xfffd or unich in urt_wa:
                    continue
                urt_wa[unich] = csetch

                self._testpoint(csetch, unich)