Go to Notification Settings
From the merchant portal, choose Settings from the navigation menu, and Notifications from the dropdown menu.
Choose a Notification to Test
Find the section for Customer Emails or Admin Notifications (whichever one you would like to test) and then click on the name of the notification, which will be shown in blue text. In the example, I am testing the Welcome Email.
Send Test Email
After clicking the blue text, the Notification Editor will pop up. Press the blue Send Test Email button at the bottom, and a test email will be sent to the email address on file for your store.