use Test;
  ...
  use My::Module;
  use Test::Resub qw(resub);
  use IO::Socket::INET;

  # test open_socket_to
  {
    my $rs = resub 'IO::Socket::INET::new', sub { 'a socket' }, capture => 1;
    my $socket = My::Module->open_socket_to(
      machine => 'example.com',
      port => '-29',
    );

    # return value of ->open_socket_to is whatever IO::Socket::INET::new gives us
    ok( $socket, 'a socket' );

    # We created the socket correctly - the fact that we provided an
    # illegal PeerPort doesn't need to be handled by this test:
    # IO::Socket::INET should have his own tests for his ->new.
    is_deeply( $rs->named_method_args, [{
      PeerAddr => 'example.com',
      PeerPort => -29,
      Proto => 'tcp',
      Type => SOCK_STREAM,
    }] );
  }