I wrote:

!be_issuffix( op->o_bd,&op->o_req_ndn ) which looks to me like a test for whether this function is _not_ to be called for this database.

No, that's a test if the DN is the exact suffix, not if it has the suffix. Anyway, for what it's worth "make test" succeeds with an "assert(0)" after the !be_issuffix test.