fails:String#unpack with directive 'w' ignores whitespace in the format string
fails:String#unpack with directive 'w' calls #to_str to coerce the directives string
fails:String#unpack with directive 'w' raises a TypeError when passed nil
fails:String#unpack with directive 'w' raises a TypeError when passed an Integer
fails:String#unpack with directive 'w' raises an ArgumentError when the format modifier is '_'
fails:String#unpack with directive 'w' raises an ArgumentError when the format modifier is '!'
fails:String#unpack with directive 'w' decodes a BER-compressed integer
fails:String#unpack with directive 'w' ignores NULL bytes between directives
fails:String#unpack with directive 'w' ignores spaces between directives
