fails:Net::FTP#chdir writes the 'CWD' command with the passed directory to the socket
fails:Net::FTP#chdir returns nil
fails:Net::FTP#chdir raises a Net::FTPPermError when the response code is 500
fails:Net::FTP#chdir raises a Net::FTPPermError when the response code is 501
fails:Net::FTP#chdir raises a Net::FTPPermError when the response code is 502
fails:Net::FTP#chdir raises a Net::FTPTempError when the response code is 421
fails:Net::FTP#chdir raises a Net::FTPPermError when the response code is 530
fails:Net::FTP#chdir raises a Net::FTPPermError when the response code is 550
fails:Net::FTP#chdir when switching to the parent directory sends the 'CDUP' command to the server
fails:Net::FTP#chdir when switching to the parent directory returns nil
fails:Net::FTP#chdir when switching to the parent directory does not raise a Net::FTPPermError when the response code is 500
fails:Net::FTP#chdir when switching to the parent directory raises a Net::FTPPermError when the response code is 501
fails:Net::FTP#chdir when switching to the parent directory raises a Net::FTPPermError when the response code is 502
fails:Net::FTP#chdir when switching to the parent directory raises a Net::FTPTempError when the response code is 421
fails:Net::FTP#chdir when switching to the parent directory raises a Net::FTPPermError when the response code is 530
fails:Net::FTP#chdir when switching to the parent directory raises a Net::FTPPermError when the response code is 550
