CD Speed and it's Write Transfer test

Has anyone run into an explanation of what the Write test, on a blank CD actually checks for. I see, after running some write transfer tests on various blank media, that some make it to 40x and some don’t. Normally ends with a 030C00 (Write Error).
But since the laser is not on, I wondered just what ‘error’ is seen.
No data is written so what is the simulated write failure. Nothing is burned to the CD so how does it detect an error?
I have never seen this written on the CD Speed site. But have not scoured it. Anyone know this?