Warning for every test since SQLAlchemy==1.3.17

Description

In SQLAlchemy==1.3.17, a change was made (https://docs.sqlalchemy.org/en/13/changelog/changelog_13.html#change-7a6fdf5e0595f654572e4f8edb32b48c).

When using pytest, flask, sqlalchemy and pytest-flask-sqlalchemy, (requirements.txt) the following warning occurs for every test.

SAWarning: Reset agent is not active.  This should not occur unless there was already a connectivity error in progress.

This warning does not happen in the normal execution of the program.

Expected behavior

No warnings present.

How to reproduce

This issue can be reproduced with the code example here.

pytest output

$ pytest 
======================================= test session starts ========================================
platform linux -- Python 3.8.0, pytest-6.0.0, py-1.9.0, pluggy-0.13.1
rootdir: /home/mia/workspace/flaskdb, configfile: setup.cfg, testpaths: tests
plugins: mock-3.2.0, flask-sqlalchemy-1.0.2
collected 2 items                                                                                  

tests/test_flaskdb.py ..                                                                     [100%]

========================================= warnings summary =========================================
tests/test_flaskdb.py::test_insert_a
tests/test_flaskdb.py::test_insert_b
  /home/mia/.virtualenvs/flaskdb/lib/python3.8/site-packages/sqlalchemy/pool/base.py:884: SAWarning: Reset agent is not active.  This should not occur unless there was already a connectivity error in progress.
    util.warn(

-- Docs: https://docs.pytest.org/en/stable/warnings.html

[jeancochrane]

Thanks for the report and the initial discussion here! This is one of those deep SA internal issues that I find to be somewhat inscrutable. I think I’d like to try to isolate the specific operation in the plugin that’s raising this warning, and then try to get to the bottom of whether it’s due to an actual problem (e.g. we’re not rolling back sessions before closing them) or whether it’s a side effect of the neccesary amount of kludgery in this plugin (in which case we should just figure out a way to suppress this warning).

[citizen-stig]

I also noticed this warning, in all my tests, which require db_session.

Is there a way I can help with fixing it?