sub asub ( $ace, $deuce?, $trey? ) {
    say "$ace $deuce $trey";
}

use Test;

supersede sub asub( $ace, $deuce?, $trey? ) { # XXX
    die "asub";
}

my $derr;

try {
    asub( 1, 2, 3);
    CATCH { $derr = $!; }
}

ok( $derr eq "asub", "asub died" );