What exactly do you mean by test. If you mean just to see if the file takes when you edit it then your system should automatically test the file if you've saved the crontab in vi with ':wq'. Unless you've edited the crontab file in '/etc' which is a big No. You should do crontab -e as what ever user you want it to run under.
If you just mean to test the system, then just make a script that will email you something or write a log report and ask crontab to write to it every minute or something simple. Once installed I've not heard of crontab not working right.