Thank's a lot for all your responses. I know now how to solve my problem. I'll
definitely not going to commit my unit-test before my fix and publish that
because then I would have commits in the history where tests fail. But other
suggested solutions do work.
Still, all that sounds like workarounds for a lacking feature. Checkout content
to the worktree without altering the index. What do you think, couldn't that be
added as an option to checkout?
-- Chris