Test mode is meant for software developers. MS enforces a very strict digital verification for drivers
and system files in vista and 7, its not advisable to turn this off because it compromises the stability and security of the OS. The problem is digital certificates cost money and in any case developers cant keep submitting every single beta they build to MS. Hence the test mode.
Although F8 is a very painful way of going about it and there are tools available which add the unverified signature to the required system files.