fails:String#center with length, padding returns a new string of specified length with self centered and padded with padstr
fails:String#center with length, padding pads with whitespace if no padstr is given
fails:String#center with length, padding returns self if it's longer than or as long as the specified length
fails:String#center with length, padding taints result when self or padstr is tainted
fails:String#center with length, padding calls #to_int to convert length to an integer
fails:String#center with length, padding raises a TypeError when length can't be converted to an integer
fails:String#center with length, padding calls #to_str to convert padstr to a String
fails:String#center with length, padding raises a TypeError when padstr can't be converted to a string
fails:String#center with length, padding raises an ArgumentError if padstr is empty
fails:String#center with length, padding returns subclass instances when called on subclasses
fails:String#center with length, padding when padding is tainted and self is untainted returns a tainted string if and only if length is longer than self
fails:String#center with length, padding with width returns a String in the same encoding as the original
fails:String#center with length, padding with width, pattern returns a String in the compatible encoding
fails:String#center with length, padding with width, pattern raises an Encoding::CompatibilityError if the encodings are incompatible
