After exporting a template to Shopify, you can test it in two ways:
Preview in Shopify
Go to Shopify Admin → Settings → Notifications
Click on a template
Click Preview to see how it looks
Send a real test email
The most reliable way to test is to create a real test order in your store. This triggers the actual notification email to your inbox, showing exactly what your customers will see.
Tip: Shopify's preview can sometimes show cached content. A real test order always shows the latest version of your email.