This effectively only tells you what the E-Marker reports though, the actual capabilities of the cable are still unknown.

You can say the cable can do whatever you want on the E-Marker, its not the source of truth.

The problem is, to actually benchmark everything, voltage drop, resistance, actual bandwidth (especially at Thunderbolt 5 speeds) requires a lot of hardware.

Using a USB-C Test Controller ($13,000), connected to a Pro Keysight Infiniium oscilloscope ($258,809) is the proper way to test it. https://www.keysight.com/au/en/product/N7018A/type-c-test-co...

They are just catching up with ShowHN:

https://news.ycombinator.com/item?id=47972511

It's not actually free, it's $14 to unlock all the features.