To start testing, you need to be an Unlimited Access member. Use your original Pirates Online Account to login while you are a member.
Usually Unlimited Access Members need to signup here. But a better way is to download the Test Launcher directly as you woudn't have to go through the process of verification and geting through your email. These are the downloads for the Test Launchers are located here. I cannot write the downloads here as the ending of the link cannot be written in the blog because of a Spam Filter, so this is the link to an old page where the link was located.
When you have started testing you can still play in Pirates Online Test through the Test Launcher even if you don't have membership or have been banned.