=== copy the DB_CONFIG file to the db dir and change the owner
whatever# cp /usr/local/etc/openldap/DB_CONFIG /var/db/openldap-data/ && chown ldap:ldap /var/db/openldap-data/DB_CONFIG

=== run the slaptest
whatever# slaptest                                                                
bdb_db_open: DB_CONFIG for suffix dc=whatever,dc=local has changed.
Performing database recovery to activate new settings.
bdb_db_open: Recovery skipped in read-only mode. Run manual recovery if errors are encountered.
bdb_db_open: db_open(/var/db/openldap-data/id2entry.bdb) failed: No such file or directory (2)
bdb(dc=whatever,dc=local): Unknown locker ID: 0
backend_startup_one: bi_db_open failed! (2)
slap_startup failed (test would succeed using the -u switch)

=== remove the DB_CONFIG file and slaptest again but gives a warning about DB_CONFIG
whatever# rm /var/db/openldap-data/DB_CONFIG
whatever# slaptest
bdb_db_open: Warning - No DB_CONFIG file found in directory /var/db/openldap-data: (2)
Expect poor performance for suffix dc=whatever,dc=local.
config file testing succeeded
whatever#