One additional note, in version 2.4.0 roundup can use a schema in a postgresql
database. issue2550852 has the discussion and links.

This allows the admin to create the database and have the roundup
user work with create schema privs not create database.

My test workflow has:

          sudo -u postgres psql -c "CREATE ROLE rounduptest_schema LOGIN PASSWORD 
'knownpasswordhere';" -U postgres
          sudo -u postgres psql -c "CREATE DATABASE rounduptest_schema;" -U postgres
          sudo -u postgres psql -c "GRANT CREATE ON DATABASE rounduptest_schema TO 
rounduptest_schema;" -U postgres

to allow creation/deletion of schemas on the database.

Granted this just pushes the grant create down a level but it fulfills the requirement
for postgres testing to use a pre-created database (if you squint hard enough).

I think running:

 python -m pytest -k "postgresql and schema" test/test_postgresql.py
 python -m pytest -k "not postgresql" test

should provide good test coverage. Patches to add markers 
(https://docs.pytest.org/en/7.1.x/example/markers.html) to make this easier
are welcome.