The captrunc test command invokes cappedTruncateAfter without a WUOW. Based on the implementation of WiredTigerRecordStore::doCappedTruncateAfter, this means that first the indexes will be detached for the deleted records and later on, the actual data will get truncated in a separate WUOW.

This means if a crash happens in between the two, the index and data will remain inconsistent.

Without a crash of the server, there is not a problem because the whole command runs with a collection X-lock.