I've been trying to run a UI test via Visual Studio Mobile center for a while now, but I'm getting the following error:
Preparing tests... failed.
Error: Cannot prepare UI Test artifacts. Returning exit code 20.
mobile-center test run uitest --app "MyAppName" --devices d5c95903 --app-path "pathToApk" --test-series "master" --locale "en_US" --build-dir "PathToBinRelease"
It sounds like you may be specifying the wrong folder for your --build-dir.
The --build-dir should be the bin/Debug folder of your Xamarin.UITest project, something like this:
Can you please try the above and let me know if it resolves the issue?