from https://developer.apple.com/videos/play/wwdc2017/505/
If you’d like to test with a large number of photos, you can generate dummy photos by https://developer.apple.com/sample-code/wwdc/2017/Creating-Large-Photo-Libraries-for-Testing.zip . Download it and run on the target device.
The app is presented in https://developer.apple.com/videos/play/wwdc2017/505/ .
~ my tech diary ~ 