SSL certificate for Active Directory (to use LDAP over SSL, aka LDAPS)

We need to support LDAPS protocol with AD, for one of our products.
Currently we use LDAP, and I understand that for LDAPS the AD server must have a certificate.
I want to do some testing for the new product with LDAPS, and for this I need some temporary certificate.
Will the free Comodo SSL certificate work for this purpose?
What is the standard procedure to obtain a certificate for an AD?