fails:String#scrub with a default replacement returns self for valid strings
fails:String#scrub with a default replacement replaces invalid byte sequences
fails:String#scrub with a custom replacement returns self for valid strings
fails:String#scrub with a custom replacement replaces invalid byte sequences
fails:String#scrub with a custom replacement replaces groups of sequences together with a single replacement
fails:String#scrub with a custom replacement raises ArgumentError for replacements with an invalid encoding
fails:String#scrub with a custom replacement raises TypeError when a non String replacement is given
fails:String#scrub with a block returns self for valid strings
fails:String#scrub with a block replaces invalid byte sequences
