Bug#40715 mtr fails when running the same test case in parallel threads

#

sub key {

  my ($self)= @_;

  my $key= $self->{name};

  $key.= "+".$self->{combination} if $self->{combination};

  return $key;

  return $self->{key};

}

sub write_test {

  my ($test, $sock, $header)= @_;

  # Give the test a unique key before serializing it

  $test->{key}= "$test" unless defined $test->{key};

  print $sock $header, "\n";

  while ((my ($key, $value)) = each(%$test)) {

    print $sock  $key, "= ";