https://www.vice.com/en_us/article/m7ezxq/how-teslas-self-driving-beta-testers-protect-the-company-from-critics

On September 14, YouTuber Galileo Russell posted a video titled "Tesla FSD V10 Monorail Test 5X ? ?." During the video, Russell set his Tesla running Full Self-Driving Beta—which is not, in fact, self-driving, but a "Level 2" driver-assistance system—on the roads under the Seattle monorail, whose support structure runs along the middle of the road. In the video, Russell is excited by how well the car handles this unique road layout and, to his mind, shows tremendous improvement.

Russell is part of a community of Youtubers with access to FSD Beta, a pre-release version of the software Tesla sells as a subscription for $200 a month. These YouTubers, called beta testers, post videos of themselves driving their Teslas around their cities, showing what FSD Beta does and doesn't do well. They're especially interested in "edge cases," scenarios drivers—and artificial intelligence—don't encounter often, to see if FSD Beta can handle them or if it gets stuck or makes potentially dangerous mistakes. Like Russell, they often use these types of "edge cases" to gauge the software's progress over time.