No need to upload duplicate images. Simply, upload the maximum size of your image say “940×600” or even higher. Contango will generate all required images automatically.
Portfolio template is a placeholder. It gets the portfolio posts and display them accordingly. So, you must have Published Portfolio Posts to view the Portfolio template in action.
As for test is concerned,
– You can test your each portfolio post before publish.
– Now (Once you published your portfolio post), you can test your Portfolio Template page before publish it.