Waymo built a bespoke, 113 acre facility for this very purpose back in 2017[0][1].
Full disclosure: Google employee, working on nothing to do with Waymo.
[0]: https://blog.waymo.com/2020/09/the-waymo-drivers-training-re... [1]: https://www.wired.com/story/google-waymo-self-driving-car-ca...