fails:String#getbyte counts from the end of the String if given a negative argument
fails:String#getbyte returns an Integer between 0 and 255
fails:String#getbyte regards a multi-byte character as having multiple bytes
fails:String#getbyte mirrors the output of #bytes
fails:String#getbyte interprets bytes relative to the String's encoding
fails:String#getbyte returns nil for out-of-bound indexes
fails:String#getbyte regards the empty String as containing no bytes
fails:String#getbyte raises a TypeError unless its argument can be coerced into an Integer
