$ cat 641197-2.t
use strict;
use warnings;
use Test::More qw(no_plan);

sub f {
    my $i = shift;
    print "ok $i\n";
    return $i < 2 ? 1 : f($i-1) + f($i-2);
}

f(3);
__END__

$ prove 641197-2.t
641197-2....# No tests run!
641197-2....ok 1/0Confused test output: test 2 answered after test 3
Test output counter mismatch [test 4]
Test output counter mismatch [test 5]
641197-2....dubious
        Test returned status 255 (wstat 65280, 0xff00)
FAILED--1 test script could be run, alas--no output ever seen