I drove 68MPH on the highway the other day. Doesn't mean it was legal.....

I hate to quote regs, but here we go:
121.547 (Admission to flight deck)
(c) "No person may admit any person to the flight deck unless there is a seat available for his use in the passenger compartment, except
(3) a CERTIFICATED airman employed by the certificate holder whose duties require an airman certificate
(4) a CERTIFICATED airman employed by another part 119 certificate holder whose duties with that part 199 certificate holder require an airman certificate...."

You are not certified to fly the airplane until you pass your checkride. Therefore, you are not certificated for that operation.