Transactions being wrongly shared across requests in tests

[calpaterson]

Description

Somewhere along the line, something has gone wrong and the session lifetime in tests not crosses multiple requests

Steps to reproduce

1. Find a test that POSTs something and then GETs it
2. Remove the sesh.commit() from the relevant system code

Expected result

Test fails

Actual result

Test passes

Additional details

https://github.com/calpaterson/csvbase/blob/67ed93c66bd427db318d46cf176443a59b65fb53/csvbase/web/main/bp.py#L1199 is a good candidate, when run in conjunction with the registration tests