It should do updates of the form
to establish the relative commit order of transactions executed by the different worker threads. Including the number of documents to be updated as part of the transaction makes it possible that at any point in time, a consistent snapshot of the database should see both (1) a consistent order of elements in the "order" array and (2) exactly nDocs containing that element. These properties should be checked as part of the $config.teardown() function after all of the transactions have completed.
SERVER-34294 will be follow-up work to have these properties checked periodically while varying the read concern level via another state function.