As proposed here:

• Consider releasing a 0.65 with some forwards compatibility for 1.0 simonw/datasette#2335 (comment)

from datasette_test import Datasette

ds = Datasette(
    plugin_config={"datasette-extract": "..."},
    permissions={"manage-secrets": {"id": "admin"}}
)

Where that permissions= thing uses config={"permissions": ...} for Datasette 1.0a+ and some more complex plugin-based mechanism for <1.0.