What tests needs to be performed post upgrade?

Hi, we are putting together an upgrade procedure for our gitlab CE install and I am looking for advice on what tests would be advisable to be ran post upgrade?

We have created replica environment of our current Prod environment and going to test upgrade on it
Currently we are using GitLab Community Edition [15.11.0]
we must follow the upgrade path below to upgrade GitLab:
15.11.13 → 16.3.7 → 16.7.8 → 16.11.6 → 17.1.2

What test we can perform ensure that application is working fine