The example suffix contains a number of people. If you look up the entry for one of those people, Barbara Jensen, either anonymously or as Directory Manager, the test_bind() plug-in function is never called. The plug-in therefore never logs informational messages to the errors log.
Run a search that bypasses the plug-in.
$ ldapsearch -h localhost -p 1389 -b dc=example,dc=com uid=bjensen sn version: 1 dn: uid=bjensen, ou=People, dc=example,dc=com sn: Jensen $ grep test_bind /local/ds/logs/errors $
Notice that the server bypasses preoperation bind plug-ins when special users request a bind.