fails:String#chars passes each char in self to the given block
fails:String#chars returns self
fails:String#chars is unicode aware
fails:String#chars returns characters in the same encoding as self
fails:String#chars works with multibyte characters
fails:String#chars works if the String's contents is invalid for its encoding
fails:String#chars returns a different character if the String is transcoded
fails:String#chars uses the String's encoding to determine what characters it contains
fails:String#chars returns an array when no block given
