To turn on the expression tester, click on Settings > Expression tester.
The expression tester will display as a bar at the bottom of the page. You can type any placeholders or functions into the top half, and the result will display in the bottom half.
As you start to type the placeholder name, you will be offered suggestions.
If the text you have entered will not work in a placeholder, Senta will display an error message in red.
The expression tester is dependent on which page you open it on. If you want to test whether placeholders will work in the context of a specific job, then you should open the expression tester on the page where you are viewing that job, or job template.