I needed to test a method that uses perl's syswrite on a socket, so my first thought was "pipe." But perl's pipe() threatened me with "Perl's pipes use IO buffering..." so I used POSIX::pipe instead which returns numeric fds. But syswrite wants filehandles. So I did this:

my ($read_fd, $write_fd) = POSIX::pipe();
open(my $read_fh, "<&=$read_fd") or die "fdopen for read: $!";
open(my $write_fh, ">&=$write_fd") or die "fdopen for write: $!";
$write_fh->blocking(0);
...
$client->{sock} = $write_fh;
...
$client->_syswrite($topic, $msg)
...
ok( sysread($read_fh, $buf, length($msg)), length($msg) );
[download]