Switching out system might not be possible.

use Test::More tests => 4;
use IO::Handle;
use Test::Fork;

pipe( GETPID, SENDPID );
SENDPID->autoflush(1);

$^F = fileno(SENDPID)
  if ( $^F < fileno(SENDPID) );
push my @cpid, fork_ok(
    1,
    sub {
        close(GETPID);
        $^F = fileno(SENDPID)
          if ( $^F < fileno(SENDPID) );
        my $r =
          system( 'lsof -np $$; echo $$ >&'
              . fileno(SENDPID)
              . '; exec src/ihlt >&2' );
        ok( $r == 2, 'ihlt: quit' );
    }
);
close(SENDPID);

if ( !$cpid[-1] ) {
    warn 'music died.';
    exit(2);
}

use IO::Socket::INET;

# create a connecting socket
my @sockets;
for ( 0 .. 2 ) {
    push @sockets,
      new IO::Socket::INET(
        PeerHost => '127.0.0.1',
        PeerPort => '2020',
        Proto    => 'tcp',
      );
    unless ($socket) {
        kill 'SIGINT', <GETPID>;
        fail "cannot connect to the server $!\n";
        die;
    }
    pass("$_: connected to the server\n");
}

my $response = "";

# data to send to a server
$sockets[0]->autoflush(1);
ok( $sockets[0]->send("Hello world!\n") == 13, 'first msg sent' );
ok( $sockets[1]->recv( $response, 1024 ) == 13, 'first msg recv' );
ok( $sockets[2]->recv( $response, 1024 ) == 13, 'first msg recv again' );

$sockets[2]->autoflush(1);
ok( $sockets[2]->send("Hello world!\n") == 13, 'first msg sent' );
ok( $sockets[1]->recv( $response, 1024 ) == 13, 'first msg recv' );
ok( $sockets[0]->recv( $response, 1024 ) == 13, 'first msg recv again' );

$sockets[$_]->close() for ( 0 .. 2 );

kill 'SIGINT', <GETPID>;