How will the extension with additional software be tested?

Hello. My extension communicates with the user’s PC. How will such an extension be validated and what are the limitations? Thank you

Twitch doesn’t only validates the stuff that is uploaded to their servers.

Which is the front end HTML/JS/CSS

You might need to provide test tools/data replay so that they can test extension functionality.

Since if the extension does nothing without the App that installed to a users PC being installed they can’t validate the extension, and you shouldn’t expect or require the validator to install said app in order to test/pass extension review.