You can test CKShares and all other CloudKit related stuff using the development environment. You need to declare in your entitlements file that you are using the development environment, not production (for both, iCloud AND APNS for push notifications).
I'm running into the same issue. I've enabled my entitlements for CloudKit and APNS, but where do you distinguish production vs development? I'm only in development mode at this time, I do not have a production worthy app yet.
XCode v. 10.2.1
Thanks in advance!