Since `#user_username` is an ID (and therefore unique in the DOM), it should be sufficient to say `within(:css, "#user_username")` -- you shouldn't need the error class.  (All you're trying to do here is make sure you're getting an error associated with username, as opposed to email or password, etc.  Targeting `#user_username` is enough to test this.) 

Same goes for the other `within` blocks.