use Test::More tests => 14;

sub digit_sum_is_odd {
   my $input = shift;
   my @digits = split //, $input;
   my $sum;
   $sum += $_ for @digits;
   return $sum % 2;
}

ok     digit_sum_is_odd(1);
ok not digit_sum_is_odd(2);
ok     digit_sum_is_odd(3);
ok     digit_sum_is_odd(9);
ok     digit_sum_is_odd(10);
ok not digit_sum_is_odd(11);
ok     digit_sum_is_odd(12);
ok not digit_sum_is_odd(13);
ok     digit_sum_is_odd(1000000);
ok not digit_sum_is_odd('pony');
ok     digit_sum_is_odd('pony1');
ok     digit_sum_is_odd(3, 4);
ok     digit_sum_is_odd(3, 5);
ok     digit_sum_is_odd(3, 'chimpanzee', 'monkey', 'baboon');