I would like to test my code for security holes what can I use to do this?

You could make a copy of your site and database and then attempt to do sql injections and cross site scripting attacks against it. Having made a copy would mean that you wouldn't mess up anything on your live site.

You've probably already covered the holes you are capable of exploiting, so testing it yourself would be meaningless.

I suggest you make a cc, upload it to a blank account and ask people on forums like this to 'hack' you, or you could hire a freelancer with good PHP knowledge to do the testing.