6.13. My own test functions - improved

It would be better if we could eliminate the multiple occurance of is

use Test::More tests => 2;
my_test(2, '+', 3, 5);
my_test(4, '+', 4, 10);


sub my_test {
   my ($x, $op, $z, $expected) = @_;

   # do stuff

   is($result, $expected);
}