use utf8 ();
sub verify_upgraded_length {
  my($s) = @_;
  # wrong
  # my $u = utf8::upgrade($s);
  my $u = $s;
  utf8::upgrade($u);
  return length($s) == length($u);
}
sub verify_downgraded_length {
  my($s) = @_;
  # wrong
  # my $d = utf8::downgrade($s);  # dies if downgrade not possible
  my $d = $s;
  utf8::downgrade($d);  # dies if downgrade not possible
  return length($s) == length($d);
}