LDAP test pass when LDAP admin user is expired
When your LDAP Administrator password has expired the LDAP connection test pass when all the LDAP users aren't able to login.
Workaround: renew the LDAP Administrator password (or the user used to integrate with redmine) or set the password noexpiry option
Redmine version 3.1.1.stable
Ruby version 1.9.3-p551 (2014-11-13) [x86_64-linux]
Rails version 4.2.4
LDAP SAMBA 4 in AD mode