The history store is used in conjunction with non-timestamped tables in two situations: (1) when a transaction commits during a checkpoint and part of it appears on disk, RTS uses the history store to retrieve the prior values to roll it back; and (2) if a page is evicted while a reader is holding a sufficiently old snapshot open, the history store is used to service that reader.

Case (1) is tested, though not that extensively (e.g. in test_checkpoint_snapshot05) but case (2) is, as far as I know, not tested at all in the Python tests.

The associated patch adds a new test hs30 that checks this behavior for both logged and unlogged tables.