Each project of the CMDB and Discovery implementation and upgrade is very unique and not repeating from one client to another. The simple hint on how to come up with the list of Test Cases related to your instance upgrade as follows: in high level write down the CMDB and Discovery objects that being managed and monitored within your pre-upgrade system. That list of objects should consist of customized or used as oob:
For CMDB: CI tables, classes, categories, business rules, client script, UI actions, ACLs, UI policy, Data policy, various types, views, forms, links, reference fields, relationships, reports, baselines, etc.
For Discovery: various attributes and properties of MID server; Discovery: Credentials, Properties; Schedules; Behaviors; IP Range Sets; Probes and Sensors; etc.
Data Integrations: various attributes and properties of SCCM and/or other similar data-integrations.
The list of your Test Cases should include your system pain-points before upgrade, etc.
Good Luck.
