Add some unit tests for the instance group

Part of blueprint decouple-nested
Change-Id: I46c18a5545658a3a10c9eb3e9a6d1511bbe7a518
Add proper unit tests for group Tags

Part of blueprint decouple-nested
Change-Id: Ib3a561c01a32bf6a118f06cf244632aa8c8a3922
Merge "Add some unit tests for the instance group"
Merge "Add proper unit tests for group Tags"