Earlier quoted context omitted.
What do you mean "testing" it, reading hardcoded data from e-marker chip, or really test it? The later would require multi-thousands dollar machine.
I'm curious as to why it is so expensive? Admittedly I know very little about electronics, and naturally the validation testing that a cable manufacturer does is going to be more thorough, but for consumer-grade testing couldn't we just have an FPGA or microcontroller scream the fibonnaci sequence in one end and another listen for the fibonnaci sequence on the other end? Sort of like memtest but instead ramping up sp…
For a "regular" USB C that supports USB 2.0 speeds (and is rated for 60W and therefore lacks an internal e-marker chip), there's just 5 wires inside: Two for data, two for power, and one for CC. There's nothing particularly complex about testing those wires for end-to-end continuity (like a cheapo network cable tester does).
A charging-only cable requires only 3 wires.
But fancier cables bring fancier functions. Do you want to test if the cable supports USB 3? With one lane, or two lanes? USB 4? Or what of the extra bits supporting alt modes like DisplayPort and MHL and the bag of chips that is Thunderbolt -- does that need all tested, too? (And no, that earlier 120Gbps figure isn't a lie.)
And power? We're able to put up to -- what -- 240W through some of these cables, right? That's a beefy bit of heat to dissipate, and those cables come with smarts inside of them that need negotiated with.
I agree that even at extremes, it's still somewhere within the realm of some appropriate FPGA bits or maybe a custom ASIC, careful circuit layout, a big resistor, and a power supply. And with enough clones from the clone factories beating eachother up on pricing, it might only cost small hundreds of dollars to buy.
So then what? You test the fancy USB-C ThunderBolt cable with the expensive tester, and pack it up for a trip for an important demo -- completely assured of its present performance. And when you get there, it doesn't work anyway.
But the demo must proceed.
So you find a backup cable somewhere (hopefully you thought to bring one yourself, because everyone around you is going to be confused about whatever it is that makes your "phone charger" such a unique and special snowflake that the ones they're trying to hand to you cannot ever be made to work), plug that backup in like anyone else would even if they'd never heard the term "cable tester," and carry on.
The tester, meanwhile? It's back at home, where it hasn't really done anything but cost money and provide some assurances that turned out to be false.
So the market is limited, the clone factories will thus never ramp up, and the tester no longer hypothetically costs only hundreds of dollars. It's right back up into the multiple-$k range like the pricing for other low-volume boutique test gear is.
(I still want one anyway, but I've got more practical things to spend money on...like a second cable to use for when the first one inevitably starts acting shitty.)