How can you 100% securely test a USB flash rive for its content ?

Hello,

many times, fresh USB flash drives from reputable tech stores - had tojan/virus files already installed inside them.

Can anyone help with a short guide, How can you 100% securely test a USB drive for its content (using your OWN computer), just to "see" the content is enough (I am not refering to scanning the files)? I refer to Windows 7 or 10.

I want to prevent the situtation where i have to trust in that my AntiVir tool will detect the virus. I want to prevent any contact of the USB files with my System, while I see what is insude.

Thank you all!