fails:String#rstrip returns a copy of self with trailing whitespace removed
fails:String#rstrip returns a copy of self with all trailing whitespace and NULL bytes removed
fails:String#rstrip taints the result when self is tainted
fails:String#rstrip! modifies self in place and returns self
fails:String#rstrip! modifies self removing trailing NULL bytes and whitespace
fails:String#rstrip! returns nil if no modifications were made
fails:String#rstrip! raises a RuntimeError on a frozen instance that is modified
fails:String#rstrip! raises a RuntimeError on a frozen instance that would not be modified
