fails:String#setbyte returns an Integer
fails:String#setbyte modifies the receiver
fails:String#setbyte changes the byte at the given index to the new byte
fails:String#setbyte allows changing bytes in multi-byte characters
fails:String#setbyte can invalidate a String's encoding
fails:String#setbyte regards a negative index as counting from the end of the String
fails:String#setbyte raises an IndexError if the index is greater than the String bytesize
fails:String#setbyte raises an IndexError if the nexgative index is greater magnitude than the String bytesize
fails:String#setbyte sets a byte at an index greater than String size
fails:String#setbyte does not modify the original string when using String.new
fails:String#setbyte raises a RuntimeError if self is frozen
fails:String#setbyte raises a TypeError unless the second argument is an Integer
