After invoking the close() function in lib/ldapauth.js, node will not terminate normally because _adminClient and _userClient are still bound. I suggest to rewrite the code in order to unbind both clients. Suggestion (not very good because it does not regard errors when unbinding _adminClient):

LdapAuth.prototype.close = function (callback) {
 var self = this;
  self._adminClient.unbind(function (err) {
    self._userClient.unbind(function (err2) {
       callback(err2) });})

By the way, I have not seen that _adminBound is set to true, therefore I think that in the current close() function, the _adminClient will never be unbound.