The title of this article intentionally omits what upgrade is being considered. Do you want to deploy a new D2000 version onto existing hardware? Or are you preparing a generational change of hardware or switching to virtualized servers in the ICT environment after four (six, eight ... sometimes ten) years? There are multiple possible scenarios – let's look at the complications with testing.
This is a companion discussion topic for the original entry at https://d2000.ipesoft.com/blog/how-to-test-before-upgrade/