Question: vpn security testing tools and info?

Hi,
 
My apologies if this is some kind of a FAQ (if it is, please send a pointer to the appropriate document) or if this is not an appropriate forum for such a question. 

I need to test the security of a (new) VPN implementation in my company. What tools would one use for such a testing,
what types of tests are typically performed, what should one look for (most common implementation mistakes, etc.), and where can one find more information on such matters (how-to documents, etc). 

Thank you in advance,
John