This kind of low level testing can be such a pain. Its fortunate this hardware has netboot. This is the "easy" path for low level testing, I've worked with other stuff where the only option is virtual SD card devices and ... damn its a pain... you end up with devices like this https://hackaday.com/2014/06/08/the-in-circuit-sd-card-switc... or when you're lucky and have more budget, devices like the SDWire ( https://badgerd.nl/sdwirec/ or https://shop.3mdeb.com/shop/open-source-hardware/sdwire/ which are both based on an older Tizen dev team design)