The isolation provider `install()` method is now passed a
`should_upgrade` argument, which is read from the settings and
represents the user decision about updates.
The tests have been updated to reflect these changes.
They ideally should find their way by themselves.
> You don’t need to import the fixture you want to use in a test,
> it automatically gets discovered by pytest. The discovery of fixture
> functions starts at test classes, then test modules, then conftest.py
> files and finally builtin and third party plugins.>
>
> — [pytest docs](https://docs.pytest.org/en/4.6.x/fixture.html#conftest-py-sharing-fixture-functions)
