Add a few extra test cases and test functions for the collaboration
model to get everything covered by tests (except for error handling, as
we cannot suddenly mock errors from the database).
Co-authored-by: Gusted <postmaster@gusted.xyz>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/825
Co-authored-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>