test_buffer: Use model objects in tests and drop validate proxy
Depends on !946 (closed)
Related to #2494 (closed)
Test Plan
tox
Migrated from D3512 (view on Phabricator)
Staging instance, all changes can be removed at any time
Depends on !946 (closed)
Related to #2494 (closed)
tox
Migrated from D3512 (view on Phabricator)