Testing version 1.6.0p8 parallel with 1.5.0.p16

Hello,
I have a similar situation regarding upgrade procedure.

I have in production 1.5.0.p21 CEE and I would like to test the latest stable version.
Can i configure a new server with the same version of production-1.5 (backup-restore method) then upgrade on the test machine and keep alive in parallel with the prod environment?

Can be a problem with the license?

Thank you,
Robert