fails:String#unpack with format 'U' calls #to_str to coerce the directives string
fails:String#unpack with format 'u' calls #to_str to coerce the directives string
fails:String#unpack with format 'u' decodes an empty string as an empty string
fails:String#unpack with format 'u' decodes the complete string ignoring newlines when given a single directive
fails:String#unpack with format 'u' appends empty string to the array for directives exceeding the input size
fails:String#unpack with format 'u' ignores the count or '*' modifier and decodes the entire string
fails:String#unpack with format 'u' decodes all ascii characters
