You can build your project by forking this CodePen pen. Or you can use this CDN link to run the tests in any environment you like: https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js
you can use the link in your pen by adding it in the pen options as a source for your javascript
or add the script tag found in the linked pen as last thing of your html box (script tags usually go at the end of the body element, but as codepen just wants the content of the body element in the html box, you can just put the script tag as last thing in there)