FSMO roles - Testing Upgrading Domain from 2003 to 2012

Hi all,

*** I have been reading links posted on other threads, Microsoft docs, etc, but could not find info to my question *****

Production env.:

2x Physical DCs on site (Windows Server 2003 R2)

1x Virtual DC on DR site (Windows Server 2003 R2)

Forest/Domain Level: Windows Server 2003

Instead of hijacking somebody else's thread, I would like to ask the following (probably a silly question):

I have P2V one of the physical DCs into a test environment. This DC holds all FSMO rolesbut"DOMAIN ROLE".

Would it be okay to try to introduce the 2012 box to the environment or do I need to P2V the other DC to have all DCs and roles online when introducing the 2012 box??

Comments are much appreciated.