Respectfully disagree. "User cannot log in as root if root user is disabled" is absolutely a test case that should be written regardless of previously seeing the bug.
Meh, you're probably right. If nothing else, I'd want to verify the result of trying to use a disabled account (text in the dialog is localized, et. al.) Run through the scenario before I formally write the case and...WTF? Yeah, I could see that.
