There are no tests for mypy.plugins.proper_plugin

There don't seem to be any tests for mypy.plugins.proper_plugin, which was manually tested for its addition in https://github.com/python/mypy/pull/16036.

Since mypy apparently owns this code, we should test it.

I've figured out this works as a unit test except that we can't import mypy.types in a unit test.

[case properPlugin]
# flags: --config=tmp/foo.ini
from mypy.types import Type, CallableType
result: Type | None = None
isinstance(result, CallableType)                      
[file foo.ini]
\[mypy]
plugins=mypy.plugins.proper_plugin
[builtins fixtures/isinstancelist.pyi]

I've recently realized this plugin parents its notes wrong, so I'd like to include a regression test for that, but I am having a hard time figuring out how to trigger it.

Inizia con mypy.plugins.proper_plugin e il caso di test unitario fornito, quindi analizza come attivare il comportamento delle note associate al genitore errato. Conferma in che modo la limitazione di importazione di mypy.types influisce sulla configurazione dei test e considera il lavoro completato quando i test coprono il plugin e lo scenario di regressione.