Resistance measurements can cursorily test claims of 240W but resistance changes with temperature which changes with current...so unless your tester puts 5 amps down the wire for 5 minutes and then tests resistance it's not a very good test.
For home use I've ended up treating real capability as an empirical property of the specific cable+port+device combo: does this exact cable drive this monitor at the mode I want, under load, for an hour? If yes, it gets a colored heat-shrink band and never leaves that use case. Everything else is a phone/charge cable until proven otherwise.
You need to generate a precise, calibrated, 40GHz signal, transmit it, then precisely measure the returned signal for phase, amplitude, and waveform integrity -at that speed.
Oscilloscopes and logic analyzers that run at that speed, are damn expensive.
I throw out every usb cable that comes bundled with devices because they are literal junk.