This is largely known as the best test site in Europe. Youtube will auto translate from German in English, should you require. And yes, that apparatus is squirting water on to the disc brakes and measuring the reduction in braking force in newtons. Ja, the Germans are quite serious.
The full article can be purchased for €4.5 here:
https://www.test.de/E-Bike-Test-4733...urzurl.e-bikes