pathing rewrite broke the contract that Config.get_template_directory() is supposed to be canonical source of templates. tests were missing

[bus-dedup]

Describe the bug
My dead simple flask app is broken after upgrade from 1.15.2 to 1.16.0. Previously, flask db init just worked and now it fails with Error: No such template <app>/lib/python3.11/site-packages/alembic/templates/flask. The template in question is located at <app>/lib/python3.11/site-packages/flask_migrate/templates/flask however, and somehow the older version of alembic was able to find it.

Apologies for a brief bug report, I am on the road right now so can't debug further. This seems to be important enough to report ASAP however.

[zzzeek]

guess we never tested this method

[sqla-tester]

Mike Bayer has proposed a fix for this issue in the main branch:

honor get_templates_path() first https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/5920