> In oss_check_closed.diff, you might want to add tests for the other
> methods as well.

I've added checks for other methods (not all of them, there are quite a few). I've also added a check for the mixer object.

> You may add parenthesis around the second s

Done.

> I still don't understand these checks

Me neither.
Since I don't know anything about Windows, I tried to keep the existing checks, but this doens't make much sense to me. Maybe Amaury can shed a light on this?