Sorry but your message is not very clear. By “AD” you mean Active Directory and you have a mapping between a XWiki group (“XWiki.TEST”) and an Active Directory group ?
If that’s the case you may have misunderstood the way the group synchronization work in the LDAP authenticator: you don’t get a copy of the LDAP group, only the user currently logging in is added (or removed) to the XWIki groups associated to LDAP groups it’s belonging to.
So the new user you added will be added in the TEST group as soon as he logs in. Note that there is a cache of groups on XWiki side for performance reason so you might need to clear it (in the LDAP application administration) or just wait long enough (see property xwiki.authentication.ldap.groupcache_expiration in xwiki.cfg).