While working on WT-7909, I encountered a scenario where WiredTiger merge testing was green however a lot of MongoDB test failures were observed when a patch test was created for daily WT drops. The root cause was found out to be the new logic added for WT-7909 that walked session list in WT_CONNECTION_IMPL data structure. None of the existing WT tests exercise opening and closing sessions in parallel to the rollback-to-stable operation. This means we were unable to detect a bug where we inspected fields inside a WT_SESSION_IMPL struct for a session that has closed and was inactive. 

The aim of this ticket to use one of the testing framework to exercise such code paths where we inspect the session list without holding locks (e.g., _wt_txn_user_active(), _wt_gen_drain()).