In #9777 we discovered that the useradd-staticids changes were broken in krogoth. We need to develop automated testing for this to ensure we can better track when useradd changes break the staticids use-case. https://bugzilla.yoctoproject.org/show_bug.cgi?id=9777 Specifically we should add selftests to ensure that the users & groups are created with the expected id's from a static map. Furthermore we should test that the expected outcome happens when a recipe tries to create a user or group which doesn't exist in the map.
A good test case for breaking this selftest is Bug 9789. In that case, systemd-sysusers can circumvent the staticids feature, adding users and groups without checking to see if staticids have been set. This should throw some kind of warning, and would be a perfect way to test the failure.
http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=5239691cc92679609cb464c55a7435d9cd9de349