fails:File.realpath returns '/' when passed '/'
fails:File.realpath returns the real (absolute) pathname not containing symlinks
fails:File.realpath uses base directory for interpreting relative pathname
fails:File.realpath uses current directory for interpreting relative pathname
fails:File.realpath uses link directory for expanding relative links
fails:File.realpath raises an Errno::ELOOP if the symlink points to itself
fails:File.realpath raises Errno::ENOENT if the file is absent
fails:File.realpath raises Errno::ENOENT if the symlink points to an absent file
