fails:File.ftype raises ArgumentError if not given exactly one filename
fails:File.ftype raises Errno::ENOENT if the file is not valid
fails:File.ftype returns a String
fails:File.ftype returns 'file' when the file is a file
fails:File.ftype returns 'directory' when the file is a dir
fails:File.ftype returns 'blockSpecial' when the file is a block
fails:File.ftype returns 'characterSpecial' when the file is a char
fails:File.ftype returns 'link' when the file is a link
fails:File.ftype returns fifo when the file is a fifo
fails:File.ftype returns 'socket' when the file is a socket
