Issue with how to load testing script in

Hey, Hi am having an issue. Am creating a markdown previewer in codesanbox for the challenge in freecodeCamp curriculum.
How can i embed the testing script provided by freecodeCamp” and most importantly where?

Hi @ziraq-young!

Just copy and paste this in your HTML, at the very end.

<script src=""></script>

Wah, this thing just flashes the testing star icon and the kit and the disappears.
Am trying pasting it above body closing tag with no change then below html closing tag with no gain