When you want to test devices or apps in SmartThings it is the ‘developer mode’ that you need to enable. For that you hold down the ‘About SmartThings’ link in the app settings menu for several seconds. That’s the link you clicked to get to the page you showed. A ‘Developer options’ section should appear but as it is added to the page after the link you are holding you might not notice until you let go and scroll down the page.
Why they feel they need to hide developer mode is a mystery.
The ‘test mode’ in the app is something different.