Creating test cases for upgrade

I cannot emphasize enough the importance of testing prior to upgrading an Oracle database in production. Sometimes even a minor upgrade can uncover bugs or enhancements that cause application code to behave differently. Not only will you want to test the entire upgrade procedure from start to finish several times, but you will also want to create test cases as you've mentioned to test the applications supported by the Oracle database. Ensure that the application support teams have thoroughly tested after the database is upgraded, and also involve the business users if possible, since they may test different functionality that the application support teams are unaware of.