Why can't you test the Notifier email like you used to be able to?

Yes, you can still test your email notifications like always - by using the Test Email button in your notification.

This feature sends a test email to default email address of your JotForm account. If you instead want to test sending a notification to other recipients that may be set up in your notification, the only way to do that is to make an actual submission on your form, as described here:

How to properly Change and Test a New Email Recipient Address.

Please let us know if you need further clarifications or assistance, and we will be happy to help.