For WT_SESSION::verify (or other operations that need exclusive access to a file such as WT_SESSION::salvage), a change was made in WT-4070 to disallow closing trees if they are dirty and a stable timestamp is set:
/* * Don't flush data from trees when there is a stable timestamp set: * that can lead to files that are inconsistent on disk after a crash. */ if (btree->modified && !bulk && S2C(session)->txn_global.has_stable_timestamp && !__wt_btree_immediately_durable(session)) return (__wt_set_return(session, EBUSY));
daniel.gottlieb raises the point is that this change is only effective when a stable timestamp has been set. When there will be no stable timestamp and if logging is disabled, crashing during/soon after a verify could leave data inconsistent on disk.
Given that, the test above should be extended to also return EBUSY for modified, non-bulk trees when global logging is disabled.