The Email Customizer for WooCommerce suggest several ways for testing your template :
1. Send Test Email
Our plugin uses wp_mail function for sending emails. If you want to test your email template, you need correct configure your wp_mail. With the help of some plugins you can do it very easily. For example, WP Mail SMTP plugin.
2. Email Preview
This feature helps you test your email without sending any email.
More information: How to use Email Preview?
3. Export Template and test it manually
You can download your template as a HTML and test it any browser or send it manually to some email address for testing. You can find export functionality on the top right menu second option.