Use "countDocuments" instead of "count" to ensure that we get an accurate count instead of an approximate count from metadata. Otherwise, the count can be inaccurate if a TTL pass happens concurrently with the count call when the access blocker is blocking writes. In this case, the TTL delete will fail and be rolled back, but count calls before the rollback is applied will still reflect the delete.

see https://github.com/mongodb/mongo/blob/731f87f94d327f83816ae5ef99732e8993d22a92/jstests/replsets/tenant_migration_collection_ttl.js#L80