Just for the records, I settled for IPC::Open3 with a $SIG{ALRM} handler like this:

#!/usr/bin/perl -w
#
use Test::More tests => 3;
use IPC::Open3;

$script = './test1-script.pl';

eval {
    local $SIG{ALRM} = sub { die "not completed\n" };
    alarm(5);
    #----------------------- 1 ---------------------------
    $pid = open3($in, $out, $err, $script);
    print $in "q\n";
    like(<$out>, qr/^QUIT$/,"Quit");
    waitpid($pid, 0);
    #----------------------- 2 ---------------------------
    $pid = open3($in, $out, $err, $script);
    close $in;
    like(<$out>, qr/^EOI$/,"End of input");
    waitpid($pid, 0);
};
unlike($@, qr/^not completed$/, "All tests completed in time");
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which tests this script:

#!/usr/bin/perl

while(1) {
        if (eof(STDIN)) {
                print "EOI\n";
                exit;
        }
        $_ = <STDIN>;
        if (/^q/i) { 
                print "QUIT\n";
                exit;
        }
        print;
}
[download]