From the manual page:
-P prefix --directory-prefix=prefix Set directory prefix to prefix. The directory prefix is the directory where all other files and sub-directories will be saved to, i.e. the top of the retrieval tree. The default is . (the current directory).
So you need to add
-P /tmp/cron_test/ (short form) or
--directory-prefix=/tmp/cron_test/ (long form) to your command. Also note that if the directory does not exist it will get created.