German sniffer dogs detect Covid-19 with 94% accuracy

Is there a link with details about how they measured the 94%. Was it a blind test? If the trainer knows which samples had covid19, the dog can read the trainer body language.

a few covid sniffer dog stories around it seems (e.g. recent discussion here https://news.ycombinator.com/item?id=25892874), all fairly unclear about measurement though?