fails:String#ljust with length, padding taints result when self or padstr is tainted
fails:String#ljust with length, padding tries to convert length to an integer using to_int
fails:String#ljust with length, padding raises a TypeError when length can't be converted to an integer
fails:String#ljust with length, padding tries to convert padstr to a string using to_str
fails:String#ljust with length, padding raises a TypeError when padstr can't be converted
fails:String#ljust with length, padding raises an ArgumentError when padstr is empty
fails:String#ljust with length, padding returns subclass instances when called on subclasses
fails:String#ljust 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#ljust with length, padding with width returns a String in the same encoding as the original
fails:String#ljust with length, padding with width, pattern returns a String in the compatible encoding
fails:String#ljust with length, padding with width, pattern raises an Encoding::CompatibilityError if the encodings are incompatible
